ORCID Profile
0000-0002-1987-4846
Current Organisation
University of Leeds
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Publisher: American Physical Society (APS)
Date: 28-06-2004
Publisher: The Optical Society
Date: 16-09-2010
DOI: 10.1364/OE.18.020799
Publisher: American Physical Society (APS)
Date: 15-08-1995
Publisher: Optica Publishing Group
Date: 13-04-2021
DOI: 10.1364/OE.414178
Abstract: We report on both experiments and theory of low-terahertz frequency range (up to 400 GHz) magnetoplasmons in a gated two-dimensional electron gas at low ( K) temperatures. The evolution of magnetoplasmon resonances was observed as a function of magnetic field at frequencies up to ∼400 GHz. Full-wave 3D simulations of the system predicted the spatial distribution of plasmon modes in the 2D channel, along with their frequency response, allowing us to distinguish those resonances caused by bulk and edge magnetoplasmons in the experiments. Our methodology is anticipated to be applicable to the low temperature ( K) on-chip terahertz measurements of a wide range of other low-dimensional mesoscopic systems.
Publisher: IEEE
Date: 09-2019
Publisher: Springer Science and Business Media LLC
Date: 18-11-2014
DOI: 10.1038/SREP07083
Publisher: Institution of Engineering and Technology
Date: 2018
DOI: 10.1049/CP.2018.0607
Publisher: The Optical Society
Date: 30-07-2019
DOI: 10.1364/OE.27.023164
Publisher: The Optical Society
Date: 20-11-2019
DOI: 10.1364/OL.44.005663
Publisher: American Physical Society (APS)
Date: 12-06-2013
Publisher: MDPI AG
Date: 09-03-2016
DOI: 10.3390/S16030352
Publisher: AIP Publishing
Date: 29-02-2016
DOI: 10.1063/1.4943173
Abstract: We have investigated terahertz (THz) frequency magnetoplasmon resonances in a two-dimensional electron system through the direct injection of picosecond duration current pulses. The evolution of the time-domain signals was measured as a function of magnetic field, and the results were found to be in agreement with calculations using a mode-matching approach for four modes observed in the frequency range above 0.1 THz. This introduces a generic technique suitable for s ling ultrafast carrier dynamics in low-dimensional semiconductor nanostructures at THz frequencies.
Publisher: IOP Publishing
Date: 15-12-2007
Publisher: The Optical Society
Date: 23-09-2013
DOI: 10.1364/OE.21.022988
Publisher: IEEE
Date: 09-2009
Publisher: IOP Publishing
Date: 10-12-2012
Publisher: The Optical Society
Date: 27-06-2014
DOI: 10.1364/OE.22.016595
Publisher: IEEE
Date: 05-2007
Publisher: Optica Publishing Group
Date: 22-05-2009
DOI: 10.1364/OE.17.009491
Abstract: We demonstrate a framework to understand and predict the far-field emission in terahertz frequency photonic-crystal quantum cascade lasers. The devices, which employ a high-performance three-well active region, are lithographically tunable and emit in the 104-120 microm wavelength range. A peak output power of 7 mW in pulsed mode is obtained at 10 K, and the typical device maximum operating temperature is 136 K. We identify the photonic-crystal band-edge states involved in the lasing process as originating from the hexapole and monopole modes at the G point of the photonic band structure, as designed. The theoretical far-field patterns, obtained via finite-difference time-domain simulations, are in excellent agreement with experiment. Polarization measurements further support the theory, and the role of the bonding wires in the emission process is elucidated.
Publisher: AIP Publishing
Date: 29-06-2005
DOI: 10.1063/1.1968412
Abstract: We report a time-resolved investigation of the resonant absorption of far-infrared radiation and the subsequent vibrational relaxation processes in a s le of polycrystalline cytosine at 4K, using terahertz time-domain spectroscopy. The subpicosecond time resolution achieved in our experiments corresponds to a near single-cycle of far-infrared radiation, and this enables us to observe the d ed oscillations of the electric field produced by excited molecules as they decay. Furthermore, we show that the progressive absorption and subsequent emission of far-infrared radiation at the frequency of the corresponding vibrational mode can be followed directly as a function of time by means of time-partitioned Fourier transforms of the transmitted signal.
Publisher: SPIE
Date: 05-09-2014
DOI: 10.1117/12.2061433
Publisher: Springer Science and Business Media LLC
Date: 05-2019
DOI: 10.1038/S41377-019-0152-Z
Abstract: Random lasers are a class of devices in which feedback arises from multiple elastic scattering in a highly disordered structure, providing an almost ideal light source for artefact-free imaging due to achievable low spatial coherence. However, for many applications ranging from sensing and spectroscopy to speckle-free imaging, it is essential to have high-radiance sources operating in continuous-wave (CW). In this paper, we demonstrate CW operation of a random laser using an electrically pumped quantum-cascade laser gain medium in which a bi-dimensional (2D) random distribution of air holes is patterned into the top metal waveguide. We obtain a highly collimated vertical emission at ~3 THz, with a 430 GHz bandwidth, device operation up to 110 K, peak (pulsed) power of 21 mW, and CW emission of 1.7 mW. Furthermore, we show that an external cavity formed with a movable mirror can be used to tune a random laser, obtaining continuous frequency tuning over 11 GHz.
Publisher: The Optical Society
Date: 25-01-2019
DOI: 10.1364/OE.27.002248
Publisher: IOP Publishing
Date: 04-01-2017
Publisher: IEEE
Date: 05-2007
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2012
Publisher: IEEE
Date: 12-2012
Publisher: IEEE
Date: 08-2015
Publisher: IEEE
Date: 08-2015
Publisher: Springer Science and Business Media LLC
Date: 22-11-2009
Publisher: IEEE
Date: 10-2019
Publisher: American Chemical Society (ACS)
Date: 11-01-2008
DOI: 10.1021/AC701688Q
Abstract: We demonstrate the use of surface-immobilized, oriented peptide aptamers for the detection of specific target proteins from complex biological solutions. These peptide aptamers are target-specific peptides expressed within a protein scaffold engineered from the human protease inhibitor stefin A. The scaffold provides stability to the inserted peptides and increases their binding affinity owing to the resulting three-dimensional constraints. A unique cysteine residue was introduced into the protein scaffold to allow orientation-specific surface immobilization of the peptide aptamer and to ensure exposure of the binding site to the target solution. Using dual-polarization interferometry, we demonstrate a strong relationship between binding affinity and aptamer orientation and determine the affinity constant KD for the interaction between an oriented peptide aptamer ST(cys+)_(pep9) and the target protein CDK2. Further, we demonstrate the high selectivity of the peptide aptamer STM_(pep9) by exposing surface-immobilized ST(cys+)_(pep9) to a complex biological solution containing small concentrations of the target protein CDK2.
Publisher: Optica Publishing Group
Date: 21-07-2020
DOI: 10.1364/OE.395227
Abstract: A model based on carrier rate equations is proposed to evaluate the gain saturation and predict the dependence of the output power of a terahertz master-oscillator power- lifier quantum cascade laser (THz-MOPA-QCL) on the material and structure parameters. The model reveals the design rules of the pre lifier and the power extractor to maximize the output power and the wall-plug efficiency. The correction of the model is verified by its agreement with the experiment results. The optimized MOPA devices exhibit single-mode emission at ∼ 2.6 THz with a side mode suppression ratio of 23 dB, a pulsed output power of 153 mW, a wall-plug efficiency of 0.22%, and a low ergence angle of ∼6°×16°, all measured at an operation temperature of 77 K. The model developed here is helpful for the design of MOPA devices and semiconductor optical lifiers, in which the active region is based on intersubband transitions.
Publisher: Elsevier BV
Date: 05-1991
Publisher: Institution of Engineering and Technology (IET)
Date: 10-2015
DOI: 10.1049/EL.2015.2878
Publisher: AIP Publishing
Date: 02-04-2003
DOI: 10.1063/1.1565680
Abstract: Terahertz time-domain spectroscopy has been used to measure the vibrational spectra of polycrystalline purine and adenine over the temperature range 4–290 K. A number of well-resolved absorption peaks were observed in the frequency range 0.2–3.0 THz, which are interpreted as originating from intermolecular vibrational modes mediated by hydrogen bonds. We find that as the temperature is reduced, the observed absorption bands resolve into narrower peaks and some shift towards higher frequencies. We explain the temperature dependence of the spectra by the anharmonicity of the vibrational potentials and give an empirical expression to describe the frequency shift.
Publisher: IEEE
Date: 09-2013
Publisher: IEEE
Date: 08-2015
Publisher: The Optical Society
Date: 03-07-2018
DOI: 10.1364/OE.26.018423
Publisher: AIP Publishing
Date: 05-04-2011
DOI: 10.1063/1.3575201
Abstract: We report terahertz (THz) diffuse reflectance measurements of bulk powdered s les at a frequency of 2.83 THz using a narrowband quantum cascade laser. S les studied comprise polydisperse powders with absorption coefficients extending over two orders of magnitude from ∼3 cm−1 to & cm−1. Diffuse reflectance measurements are used to obtain the effective absorption coefficient of these s les from the backscattering cross-section, predicted under the quasi-crystalline approximation (QCA) in the T-matrix formulation and in conjunction with the Percus-Yevick pair distribution function. Results are compared with effective absorption coefficients obtained from THz time-domain spectroscopy measurements on pressed pellet s les, and show good agreement over the range of effective absorption coefficients studied. We observe that the backscattering cross-section predicted under the QCA is strongly dependent on both the real and imaginary components of the complex permittivity of the s le, and we show that reliable determination of the absorption coefficient from diffuse reflectance measurements therefore requires knowledge of the s le's refractive index. This work demonstrates the applicability of diffuse reflectance measurements, using a THz frequency quantum cascade laser, to the high-resolution spectroscopic analysis of bulk powdered s les at THz frequencies.
Publisher: Institution of Engineering and Technology (IET)
Date: 2005
DOI: 10.1049/EL:20050128
Publisher: American Chemical Society (ACS)
Date: 12-04-2012
DOI: 10.1021/LA300510X
Abstract: We discuss the assembly, structure, and stability of multilayer molecular films formed from multiple mercaptoalkanoic acid monolayers ligated via carboxyl and thiol interactions with alent copper ions. Using dual-polarization interferometry to study the assembly of multilayer films in real time, we observe a clear linear relationship between the number of layers within a film and the overall average film thickness. Unexpectedly, however, we find a restructuring of the lower monolayer upon association of the Cu(2+) ions to form the Cu carboxylate surface. In particular, the thickness of the lower monolayer was found to decrease significantly, accompanied by an increase in the film density. The conformation of the monolayer subsequently recovered to that observed originally following the reduction of the Cu ion to Cu(+) upon chemisorption of the adlayer. Comparable restructuring was also observed in molecular dynamics simulations of a bilayer film assembled on a gold surface. Our combined experimental and theoretical study suggests that the observed restructuring is a result of charge-charge interactions between adjacent Cu ions that exist in the +2 oxidation state in the copper carboxylate surface and in the +1 oxidation state following chemisorption of the adlayer.
Publisher: Springer Science and Business Media LLC
Date: 28-09-2018
DOI: 10.1038/S42005-018-0059-7
Abstract: Acoustoelectric devices convert acoustic energy to electrical energy and vice versa. Devices working at much higher acoustic frequencies than those currently available have potential scientific and technological applications, for ex le, as detectors in phononics experiments and as transducers in bulk acoustic wave filters at terahertz (THz) frequencies. Here we demonstrated an active acoustoelectronic device based on a GaAs heterostructure: an acoustically gated transistor or phonotransistor. Instead of being controlled in the conventional manner by an electrical signal applied to a metallic or semiconductor gate as in a high electron mobility transistor (HEMT), the drain-source current was controlled by a bulk sub-THz acoustic wave passing through the channel in a direction perpendicular to the current flow.
Publisher: SPIE
Date: 09-02-2006
DOI: 10.1117/12.659662
Publisher: Institution of Engineering and Technology (IET)
Date: 2003
DOI: 10.1049/EL:20030779
Publisher: IOP Publishing
Date: 22-08-2012
Publisher: Springer Science and Business Media LLC
Date: 24-04-2011
Publisher: American Chemical Society (ACS)
Date: 19-10-2015
Publisher: Institution of Engineering and Technology (IET)
Date: 2004
DOI: 10.1049/EL:20040102
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2017
Publisher: IEEE
Date: 09-2012
Publisher: AIP Publishing
Date: 07-03-2016
DOI: 10.1063/1.4943167
Abstract: We demonstrate strong light-matter coupling in three dimensional terahertz meta-atoms at room temperature. The intersubband transition of semiconductor quantum wells with a parabolic energy potential is strongly coupled to the confined circuital mode of three-dimensional split-ring metal-semiconductor-metal resonators that have an extreme sub-wavelength volume (λ/10). The frequency of these lumped-element resonators is controlled by the size and shape of the external antenna, while the interaction volume remains constant. This allows the resonance frequency to be swept across the intersubband transition and the anti-crossing characteristic of the strong light-matter coupling regime to be observed. The Rabi splitting, which is twice the Rabi frequency (2ΩRabi), amounts to 20% of the bare transition at room temperature, and it increases to 28% at low-temperature.
Publisher: Springer Science and Business Media LLC
Date: 17-07-2012
DOI: 10.1038/NCOMMS1958
Abstract: Symmetric and antisymmetric band-edge modes exist in distributed feedback surface-emitting semiconductor lasers, with the dominant difference being the radiation loss. Devices generally operate on the low-loss antisymmetric modes, although the power extraction efficiency is low. Here we develop graded photonic heterostructures, which localize the symmetric mode in the device centre and confine the antisymmetric modes close to the laser facet. This modal spatial separation is combined with absorbing boundaries to increase the antisymmetric mode loss, and force device operation on the symmetric mode, with elevated radiation efficiency. Application of this concept to terahertz quantum cascade lasers leads to record-high peak-power surface emission (>100 mW) and differential efficiencies (230 mW A(-1)), together with low- ergence, single-lobed emission patterns, and is also applicable to continuous-wave operation. Such flexible tuning of the radiation loss using graded photonic heterostructures, with only a minimal influence on threshold current, is highly desirable for optimizing second-order distributed feedback lasers.
Publisher: AIP Publishing
Date: 20-10-2003
DOI: 10.1063/1.1622431
Abstract: Ultralow-threshold terahertz laser emission exploiting in-plane confinement arising from perpendicular magnetic field applied on a quantum-cascade structure is reported. A special design strategy has been adopted that takes advantage of the selective opening and closing of relaxation channels by elastic scattering between Landau levels. The key effect is a reduction of the lower state lifetime of the lasing transition that produces population inversion. The structure shows laser action only with applied magnetic field and yields threshold current densities as low as 19 A/cm2 at 4.2 K and 32 A/cm2 at 60 K at a frequency of 3.6 THz.
Publisher: American Physical Society (APS)
Date: 31-10-2011
Publisher: Springer Science and Business Media LLC
Date: 2003
Publisher: AIP Publishing
Date: 18-01-2010
DOI: 10.1063/1.3273056
Abstract: The use of integrated photonic structures to tailor the behavior of light is extremely promising for optimizing performance and for introducing advanced functionalities into optoelectronic devices. We demonstrate a powerful method based on photonic-band engineering which allows the optimization of the resonator quality factors of devices operating on band-edge photonic-crystal states. We also show that carefully designed π-shifts in two-dimensional photonic-resonators give enhanced beam properties. The application of these general techniques to terahertz quantum cascade lasers yields improved maximum operating temperatures, and angularly narrow, single-lobed surface emission of ≈12°×8°. The devices operate at ≈2.8/2.9 THz, with peak output powers of 5 mW at 78 K.
Publisher: The Optical Society
Date: 25-06-2019
DOI: 10.1364/OL.44.003314
Publisher: American Physical Society (APS)
Date: 15-12-1996
Publisher: Optica Publishing Group
Date: 14-04-2008
DOI: 10.1364/OE.16.005997
Abstract: We report diffuse reflection imaging in air of concealed powdered s les using a terahertz quantum cascade laser. The sensitivity of the detection scheme to sub-surface absorption within s les is confirmed using fully-characterized powdered admixtures of polystyrene and polymethyl methacrylate (PMMA). Measurements of the backscattering intensity from these s les are then used in conjunction with Kubelka-Munk scattering theory, as well as several models based on the quasi-crystalline approximation, to extract the absorption coefficient of PMMA. Our research demonstrates the feasibility of high-resolution frequency-domain terahertz imaging for the detection and identification of concealed powders in a reflection geometry.
Publisher: AIP Publishing
Date: 06-2021
DOI: 10.1063/5.0046186
Abstract: Near-field microscopy techniques operating in the terahertz (THz) frequency band offer the tantalizing possibility of visualizing with nanometric resolution the localized THz fields supported by in idual resonators, micro-structured surfaces, and metamaterials. Such capabilities promise to underpin the future development and characterization of a wide range of devices, including THz emitters, detectors, optoelectronic modulators, sensors, and novel optical components. In this work, we report scattering-type scanning near-field optical microscopy using a THz-frequency quantum cascade laser (QCL) to probe coherently the localized field supported by in idual micro-resonator structures. Our technique demonstrates deep sub-wavelength mapping of the field distribution associated with in-plane resonator modes in plasmonic dipole antennas and split ring resonator structures. By exploiting electronic tuning of the QCL in conjunction with the coherent self-mixing effect in these lasers, we are able to resolve both the magnitude and the phase of the out-of-plane field. We, furthermore, show that the elliptically polarized state of the QCL field can be exploited for the simultaneous excitation and measurement of plasmonic resonances in these structures while suppressing the otherwise dominant signal arising from the local material permittivity.
Publisher: AIP Publishing
Date: 18-03-2002
DOI: 10.1063/1.1461054
Abstract: Electroluminescence at λ∼69 μm (4.3 THz) is reported from interminiband transitions in quantum-cascade structures with superlattice active regions. Spontaneous emission gives a low-temperature linewidth of 2 meV (0.48 THz) with linear light–current characteristics observed up to high-current densities (625 A/cm2), resulting in record output powers of 500 pW. Devices operate up to above liquid-nitrogen temperature, with both emission wavelength and current–voltage characteristics in good agreement with theoretical predictions.
Publisher: SPIE
Date: 24-10-2013
DOI: 10.1117/12.2028675
Publisher: Springer Science and Business Media LLC
Date: 12-02-2020
Publisher: Optica Publishing Group
Date: 02-08-2007
DOI: 10.1364/OL.32.002297
Abstract: The generation of terahertz (THz) transients in photoconductive emitters has been studied by varying the spatial extent and density of the optically excited photocarriers in asymmetrically excited, biased low-temperature-grown GaAs antenna structures. We find a pronounced dependence of the THz pulse intensity and broadband (>6.0 THz) spectral distribution on the pump excitation density and simulate this with a three-dimensional carrier dynamics model. We attribute the observed variation in THz emission to changes in the strength of the screening field.
Publisher: IOP Publishing
Date: 1989
Publisher: Springer Science and Business Media LLC
Date: 06-08-2018
DOI: 10.1038/S41467-018-05601-X
Abstract: Single-mode frequency-tuneable semiconductor lasers based on monolithic integration of multiple cavity sections are important components, widely used in optical communications, photonic integrated circuits and other optical technologies. To date, investigations of the ultrafast switching processes in such lasers, essential to reduce frequency cross-talk, have been restricted to the observation of intensity switching over nanosecond-timescales. Here, we report coherent measurements of the ultrafast switch-on dynamics, mode competition and frequency selection in a monolithic frequency-tuneable laser using coherent time-domain s ling of the laser emission. This approach allows us to observe hopping between lasing modes on picosecond-timescales and the temporal evolution of transient multi-mode emission into steady-state single mode emission. The underlying physics is explained through a full multi-mode, temperature-dependent carrier and photon transport model. Our results show that the fundamental limit on the timescales of frequency-switching between competing modes varies with the underlying Vernier alignment of the laser cavity.
Publisher: AIP Publishing
Date: 03-03-2014
DOI: 10.1063/1.4866661
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2016
Publisher: The Optical Society
Date: 29-08-2017
DOI: 10.1364/OE.25.021753
Publisher: IEEE
Date: 09-2013
Publisher: AIP Publishing
Date: 18-02-2004
DOI: 10.1063/1.1650905
Abstract: A THz (λ∼80 μm) quantum-cascade laser utilizing alternating photon- and phonon-emitting stages has been developed to achieve efficient extraction of electrons from the lower laser level. Thermal backfilling of electrons is drastically reduced leading to an operation up to 95 K and a weak temperature dependence of the power versus current slope efficiency. The threshold current density is 280 A cm−2 at 6 K and increases to 580 A cm−2 at 90 K. Peak output powers of 10 mW at 30 K and 4 mW at 80 K are obtained.
Publisher: AIP Publishing
Date: 05-08-2013
DOI: 10.1063/1.4818584
Abstract: Joule heating causes significant degradation in the power emitted from terahertz-frequency quantum-cascade lasers (THz QCLs). However, to date, it has not been possible to characterize the thermal equilibration time of these devices, since THz power degradation over sub-millisecond time-scales cannot be resolved using conventional bolometric or pyroelectric detectors. In this letter, we use a superconducting antenna-coupled niobium nitride detector to measure the emission from a THz QCL with a nanosecond-scale time-resolution. The emitted THz power is shown to decay more rapidly at higher heat-sink temperatures, and in steady-state the power reduces as the repetition rate of the driving pulses increases. The pulse-to-pulse variation in active-region temperature is inferred by comparing the THz signals with those obtained from low duty-cycle measurements. A thermal resistance of 8.2 ± 0.6 K/W is determined, which is in good agreement with earlier measurements, and we calculate a 370 ± 90-μs bulk heat-storage time, which corresponds to the simulated heat capacity of the device substrate.
Publisher: Institution of Engineering and Technology (IET)
Date: 02-2014
DOI: 10.1049/EL.2013.4035
Publisher: The Royal Society
Date: 15-01-2000
Publisher: IOP Publishing
Date: 14-10-2010
DOI: 10.1088/0957-4484/21/45/455301
Abstract: We discuss the fabrication of closely spaced nanoscale embedded co-planar electrodes with concealed contact wires, using a GaAs-based flip-chip technology. The co-planarity of the electrodes with the substrate and the low roughness of the exposed surface are achieved by templating the deposition of both the dielectric and electrode metal onto a smooth GaAs substrate. The resulting electrodes, with sizes of around 300 nm and separations as low as 25 nm, have RMS roughnesses of less than 0.2 nm and a co-planarity of around 1 nm.
Publisher: IOP Publishing
Date: 25-08-2016
DOI: 10.1088/0957-4484/27/39/395301
Abstract: We present a method for the specific, spatially targeted attachment of DNA molecules to lithographically patterned gold surfaces-demonstrated by bridging DNA strands across nanogap electrode structures. An alkanethiol self-assembled monolayer was employed as a molecular resist, which could be selectively removed via electrochemical desorption, allowing the binding of thiolated DNA anchoring oligonucleotides to each electrode. After introducing a bridging DNA molecule with single-stranded ends complementary to the electrode-tethered anchoring oligonucleotides, the positioning of the DNA molecule across the electrode gap, driven by self-assembly, occurred autonomously. This demonstrates control of molecule positioning with resolution limited only by the underlying patterned structure, does not require any alignment, is carried out entirely under biologically compatible conditions, and is scalable.
Publisher: American Chemical Society (ACS)
Date: 21-02-2020
Publisher: American Chemical Society (ACS)
Date: 31-01-2014
DOI: 10.1021/LA403983B
Publisher: Wiley
Date: 22-01-2008
Publisher: Elsevier BV
Date: 03-2002
Publisher: AIP Publishing
Date: 21-01-2008
DOI: 10.1063/1.2835705
Abstract: We demonstrate an evanescent field modality for terahertz frequency time-domain measurements, based on the interaction between a s le and the evanescent field extending above lithographically defined terahertz waveguides. We quantify this interaction using freely positionable dielectric s les (GaAs) moved in close proximity to the waveguide (a terahertz microstrip line), finding a reduction in the microstrip-propagating pulse litude and an increase in its time delay when the dielectric is brought into the microstrip evanescent field. We also show that the frequency response of resonant passive circuit elements (stub band-stop filters), integrated into the microstrip line, can be used to determine the terahertz frequency properties of scanned s les, opening the way for a terahertz subwavelength imaging modality, the resolution of which is limited by lithographic constraints, rather than by free-space diffraction.
Publisher: American Physical Society (APS)
Date: 12-12-2022
Publisher: MDPI AG
Date: 02-03-2023
DOI: 10.3390/S23052721
Abstract: To reduce the water footprint in agriculture, the recent push toward precision irrigation management has initiated a sharp rise in photonics-based hydration sensing in plants in a non-contact, non-invasive manner. Here, this aspect of sensing was employed in the terahertz (THz) range for mapping liquid water in the plucked leaves of Bambusa vulgaris and Celtis sinensis. Two complementary techniques, broadband THz time-domain spectroscopic imaging and THz quantum cascade laser-based imaging, were utilized. The resulting hydration maps capture the spatial variations within the leaves as well as the hydration dynamics in various time scales. Although both techniques employed raster scanning to acquire the THz image, the results provide very distinct and different information. Terahertz time-domain spectroscopy provides rich spectral and phase information detailing the dehydration effects on the leaf structure, while THz quantum cascade laser-based laser feedback interferometry gives insight into the fast dynamic variation in dehydration patterns.
Publisher: Optica Publishing Group
Date: 21-05-2020
DOI: 10.1364/OE.391073
Abstract: We provide an analysis of the electromagnetic modes of three-dimensional metamaterial resonators in the THz frequency range. The fundamental resonance of the structures is fully described by an analytical circuit model, which not only reproduces the resonant frequencies but also the coupling of the metamaterial with an incident THz radiation. We also demonstrate the contribution of the propagation effects, and show how they can be reduced by design. In the optimized design, the electric field energy is lumped into ultra-subwavelength (λ/100) capacitors, where we insert a semiconductor absorber based on the collective electronic excitation in a two dimensional electron gas. The optimized electric field confinement is exhibited by the observation of the ultra-strong light-matter coupling regime, and opens many possible applications for these structures in detectors, modulators and sources of THz radiation.
Publisher: SPIE
Date: 07-07-2003
DOI: 10.1117/12.475764
Publisher: Elsevier BV
Date: 02-2000
Publisher: American Physical Society (APS)
Date: 26-10-2001
Publisher: IEEE
Date: 2010
Publisher: SPIE
Date: 04-02-2013
DOI: 10.1117/12.2004125
Publisher: OSA
Date: 2018
Publisher: IOP Publishing
Date: 04-1994
Publisher: IEEE
Date: 05-2007
Publisher: OSA
Date: 2018
Publisher: IOP Publishing
Date: 29-10-2014
DOI: 10.1088/0953-8984/26/47/475801
Abstract: We have investigated experimentally the scaling behaviour of quantum Hall transitions in GaAs/AlGaAs heterostructures of a range of mobility, carrier concentration, and spacer layer width. All three critical scaling exponents γ, κ and p were determined independently for each s le. We measure the localization length exponent to be γ ≈ 2.3, in good agreement with expected predictions from scaling theory, but κ and p are found to possess non-universal values. Results obtained for κ range from κ = 0.16 ± 0.02 to κ = 0.67 ± 0.02, and are found to be Landau level (LL) dependent, whereas p is found to decrease with increasing s le mobility. Our results demonstrate the existence of two transport regimes in the LL conductivity peak universality is found within the quantum coherent transport regime present in the tails of the conductivity peak, but is absent within the classical transport regime found close to the critical point at the centre of the conductivity peak. We explain these results using a percolation model and show that the critical scaling exponent depends on certain important length scales that correspond to the microscopic description of electron transport in the bulk of a two-dimensional electron system.
Publisher: IEEE
Date: 09-2019
Publisher: AIP Publishing
Date: 21-01-2013
DOI: 10.1063/1.4789535
Abstract: We demonstrate single-mode surface-emitting terahertz frequency quantum cascade lasers utilising non-uniform second-order distributed feedback concentric-circular-gratings. The grating is designed for single-mode operation and surface emission for efficient and directional optical power out-coupling. The devices exhibit single-mode operation over the entire dynamic range with a side-mode-suppression-ratio of around 30 dB at 78 K, and a six-fold rotationally symmetric far-field pattern. In addition, the devices show a peak output power approximately three times higher than in ridge-waveguide lasers of similar size, whilst maintaining similar threshold current densities for the 3.8 THz emission and without remarkably sacrificing the maximum temperature operation performance. Owing to the high symmetry of the structure and the broad area light emission from surface, the devices are potentially very suitable for use as single-mode, high power emitters for integration into two-dimensional laser arrays.
Publisher: IEEE
Date: 09-2008
Publisher: Springer Science and Business Media LLC
Date: 22-12-2015
Publisher: Elsevier BV
Date: 08-2003
Publisher: IEEE
Date: 09-2013
Publisher: Springer Berlin Heidelberg
Date: 29-07-2003
Publisher: IOP Publishing
Date: 04-12-2002
Publisher: Elsevier BV
Date: 07-1994
Publisher: AIP Publishing
Date: 08-08-2011
DOI: 10.1063/1.3623424
Abstract: We demonstrate In-assisted desorption of native GaAs surface oxides at substrate temperatures of 480–550 °C. The oxides are removed through production of volatile Ga and In suboxides, Ga2O, and In2O. Compared to a Ga-assisted desorption process, excess In is easily removed at low substrate temperature, favouring a clean, smooth surface. The feasibility of using In-assisted desorption for the regrowth of high quality quantum dot structures is shown.
Publisher: IEEE
Date: 06-2007
Publisher: AIP Publishing
Date: 16-06-2014
DOI: 10.1063/1.4884056
Abstract: We demonstrate the operation of coupled-cavity terahertz frequency quantum-cascade lasers composed of two sub-cavities separated by an air gap realized by optical lithography and dry etching. This geometry allows stable, single mode operation with typical side mode suppression ratios in the 30–40 dB range. We employ a transfer matrix method to model the mode selection mechanism. The obtained results are in good agreement with the measurements and allow prediction of the operating frequency.
Publisher: AIP Publishing
Date: 29-02-2016
DOI: 10.1063/1.4943088
Abstract: We report two-dimensional apertureless near-field terahertz (THz) imaging using a quantum cascade laser (QCL) source and a scattering probe. A near-field enhancement of the scattered field litude is observed for small tip-s le separations, allowing image resolutions of ∼1 μm (∼λ/100) and ∼7 μm to be achieved along orthogonal directions on the s le surface. This represents the highest resolution demonstrated to date with a THz QCL. By employing a detection scheme based on self-mixing interferometry, our approach offers experimental simplicity by removing the need for an external detector and also provides sensitivity to the phase of the reinjected field.
Publisher: American Chemical Society (ACS)
Date: 14-01-2004
DOI: 10.1021/LA036027O
Publisher: AIP Publishing
Date: 21-03-2011
DOI: 10.1063/1.3571289
Abstract: We report the detection of terahertz frequency radiation using photoconductive antennas fabricated from Fe-doped InGaAs, grown by metal-organic chemical vapor deposition. Coherent photoconductive detection is demonstrated using femtosecond laser pulses centered at either an 800 or a 1550 nm wavelength. The InGaAs resistivity and the sensitivity of photoconductive detection are both found to depend on the Fe-doping level. We investigate a wide range of probe laser powers, finding a peak in detected signal for ∼5 mW probe power, followed by a reduction at larger powers, attributed to screening of the detected THz field by photo-generated carriers in the material. The measured signal from Fe:InGaAs photoconductive detectors excited at 800 nm is four times greater than that from a low-temperature-grown GaAs photodetector with identical antenna design, despite the use of a ten times smaller probe power.
Publisher: IOP Publishing
Date: 16-10-2002
DOI: 10.1088/0031-9155/47/21/302
Abstract: The terahertz region of the electromagnetic spectrum spans the frequency range between the mid-infrared and the millimetre/microwave. This region has not been exploited fully to date owing to the limited number of suitable (in particular, coherent) radiation sources and detectors. Recent demonstrations, using pulsed near-infrared femtosecond laser systems, of the viability of THz medical imaging and spectroscopy have sparked international interest yet much research still needs to be undertaken to optimize both the power and bandwidth in such THz systems. In this paper, we review how femtosecond near-infrared laser pulses can be converted into broad band THz radiation using semiconductor crystals, and discuss in depth the optimization of one specific generation mechanism based on ultra-fast transport of electrons and holes at a semiconductor surface. We also outline a few of the opportunities for a technology that can address a erse range of challenges spanning the physical and biological sciences, and note the continuing need for the development of solid state, continuous wave, THz sources which operate at room temperature.
Publisher: IEEE
Date: 05-2007
Publisher: AIP Publishing
Date: 06-06-2011
DOI: 10.1063/1.3597411
Abstract: We report the development of a scattering-type near-field scanning optical microscope (sNSOM) which operates at temperatures down to 100 K with a scanning range of up to 400 μm. We have used this sNSOM to map the electromagnetic near-field on mid-IR and terahertz (THz) surface emitting quantum cascade lasers with photonic-crystal resonators. Mid-IR devices operate at λ=7.5 μm (40 THz) while THz devices operate at λ≈110 μm (2.7 THz). The near-field images—in agreement with numerical calculations—demonstrate an instrument resolution of 100's nm.
Publisher: American Physical Society (APS)
Date: 09-08-2004
Publisher: AIP Publishing
Date: 15-09-2014
DOI: 10.1063/1.4896032
Abstract: A periodically poled lithium niobate (PPLN) crystal with multiple poling periods is used to generate tunable narrow-bandwidth THz pulses for injection seeding a quantum cascade laser (QCL). We demonstrate that longitudinal modes of the quantum cascade laser close to the gain maximum can be selected or suppressed according to the seed spectrum. The QCL emission spectra obtained by electro-optic s ling from the quantum cascade laser, in the most favorable case, shows high selectivity and lification of the longitudinal modes that overlap the frequency of the narrow-band seed. Proper selection of the narrow-band THz seed from the PPLN crystal discretely tunes the longitudinal mode emission of the quantum cascade laser. Moreover, the THz wave build-up within the laser cavity is studied as a function of the round-trip time. When the seed frequency is outside the maximum of the gain spectrum the laser emission shifts to the preferential longitudinal mode.
Publisher: AIP Publishing
Date: 27-09-2010
DOI: 10.1063/1.3489941
Abstract: Terahertz frequency photonic-crystal quantum cascade lasers allow directional and controllable surface emission while at the same time functioning efficiently well above liquid nitrogen temperature. Through an in-depth understanding of the mechanism underlying surface emission, we demonstrate optimized devices with significantly reduced absolute threshold currents. We are able to reduce the device surface area by more than a factor of two, while maintaining angularly narrow, single-lobed surface emission with a ergence of ≈10°×10°. The devices emit at ∼2.8–2.9 THz, with maximum operating temperatures in the range 80–150 K.
Publisher: Optica Publishing Group
Date: 11-2002
DOI: 10.1364/OL.27.001935
Abstract: A compact, high-power emitter of half-cycle terahertz (THz) radiation is demonstrated. The device consists of an epitaxial InAs emitter upon a GaAs prism and produces THz pulses that are 20 times more powerful than those from conventional planar InAs emitters. This improvement is a direct result of reorienting the transient THz dipole such that its axis is not perpendicular to the emitting surface.
Publisher: IEEE
Date: 08-2017
Publisher: Springer Science and Business Media LLC
Date: 2003
Publisher: AIP Publishing
Date: 20-04-2020
DOI: 10.1063/5.0004591
Abstract: Quantum cascade detectors (QCDs) are unipolar infrared devices where the transport of the photoexcited carriers takes place through confined electronic states, without an applied bias. In this photovoltaic mode, the detector's noise is not dominated by a dark shot noise process, and therefore, performances are less degraded at high temperature with respect to photoconductive detectors. This work describes a 9 μm QCD embedded into a patch-antenna metamaterial, which operates with state-of-the-art performances. The metamaterial gathers photons on a collection area, Acoll, much larger than the geometrical area of the detector, improving the signal to noise ratio up to room temperature. The background-limited detectivity at 83 K is 5.5 × 1010 cm Hz1/2 W−1, while at room temperature, the responsivity is 50 mA/W at 0 V bias. A patch antenna QCD is an ideal receiver for a heterodyne detection setup, where a signal at a frequency of 1.4 GHz and T = 295 K is reported as demonstration of uncooled 9 μm photovoltaic receivers with a GHz electrical bandwidth. These findings guide the research toward uncooled IR quantum limited detection.
Publisher: IEEE
Date: 10-2015
Publisher: AIP Publishing
Date: 20-03-2023
DOI: 10.1063/5.0142359
Abstract: Terahertz (THz) quantum cascade lasers (QCLs) have been shown to emit peak powers greater than 1 W from a single facet in a single plasmon geometry. However, this is typically achieved by increasing the laser ridge width, resulting in higher-order transverse modes, limiting the achievable power density. Here, we control and fully suppress these modes through thin metallic side-absorbers, showing laser action solely on the fundamental transverse mode operation without sacrificing high THz peak powers. This leads to enhanced power densities and electric fields of up to 1.8 kW/cm2 and 1.17 kV/cm, respectively, opening up the possibility of applying THz QCLs as pump sources for investigations of nonlinear THz physical phenomena.
Publisher: American Chemical Society (ACS)
Date: 25-02-2006
DOI: 10.1021/BM050890G
Abstract: The inherent self-recognition properties of DNA have led to its use as a scaffold for various nanotechnology self-assembly applications, with macromolecular complexes, metallic and semiconducting nanoparticles, proteins, inter alia, being assembled onto a designed DNA scaffold. Such structures may typically comprise a number of DNA molecules organized into macromolecules. Many studies have used synthetic methods to produce the constituent DNA molecules, but this typically constrains the molecules to be no longer than around 100 base pairs (30 nm). However, applications that require larger self-assembling DNA complexes, several tens of nanometers or more, need to be generated by other techniques. Here, we present a generic technique to generate large linear, branched, and/or circular DNA macromolecular complexes. The effectiveness of this technique is demonstrated here by the use of Lambda Bacteriophage DNA as a template to generate single- and double-branched DNA structures approximately 120 nm in size.
Publisher: AIP Publishing
Date: 31-08-2009
DOI: 10.1063/1.3216579
Abstract: We have measured the picosecond time-domain response of Goubau-line waveguides, formed on quartz substrates, by integrating regions of low-temperature-grown gallium arsenide into the waveguides to act both as pulsed current emitters and detectors. Using one pair of photoconductive switches for excitation and a second pair for detection, pulsed signal propagation of a low dispersion electric field mode was demonstrated in the Goubau-lines, with the signal bandwidth extending beyond 800 GHz. Furthermore, it was demonstrated that terahertz bandstop filters can be integrated into a Goubau-line for removal of specific frequencies from the transmitted pulses.
Publisher: AIP Publishing
Date: 03-04-2006
DOI: 10.1063/1.2191423
Abstract: We report on measurements of the excitation, propagation, and detection of picosecond duration electrical pulses at cryogenic (∼4K) temperatures in a microstrip circuit. A reduction is observed in the measured excitation and propagating pulse widths at low temperatures, compared with room temperature. The results indicate both that the electrical properties of low-temperature-grown GaAs make it suitable for photoconductive excitation and detection in cryogenic optoelectric circuits and that an organic polymer is a good transmissive medium for terahertz (THZ) frequency range excitations at low temperatures. This work will prove an invaluable starting point for future guided wave terahertz experiments at cryogenic temperatures.
Publisher: IEEE
Date: 09-2006
Publisher: Institution of Engineering and Technology (IET)
Date: 2006
DOI: 10.1049/EL:20064168
Publisher: Springer Science and Business Media LLC
Date: 03-03-2021
DOI: 10.1038/S41467-021-21659-6
Abstract: Millimeter wave (mmWave) generation using photonic techniques has so far been limited to the use of near-infrared lasers that are down-converted to the mmWave region. However, such methodologies do not currently benefit from a monolithic architecture and suffer from the quantum defect i.e. the difference in photon energies between the near-infrared and mmWave region, which can ultimately limit the conversion efficiency. Miniaturized terahertz (THz) quantum cascade lasers (QCLs) have inherent advantages in this respect: their low energy photons, ultrafast gain relaxation and high nonlinearities open up the possibility of innovatively integrating both laser action and mmWave generation in a single device. Here, we demonstrate intracavity mmWave generation within THz QCLs over the unprecedented range of 25 GHz to 500 GHz. Through ultrafast time resolved techniques, we highlight the importance of modal phases and that the process is a result of a giant second-order nonlinearity combined with a phase matched process between the THz and mmWave emission. Importantly, this work opens up the possibility of compact, low noise mmWave generation using modelocked THz frequency combs.
Publisher: IEEE
Date: 05-2011
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2017
Publisher: IOP Publishing
Date: 18-06-2003
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2012
Publisher: AIP Publishing
Date: 15-02-2002
DOI: 10.1063/1.1433187
Abstract: We present a theoretical treatment of surface–field THz generation in semiconductors, which explains the power enhancement observed when a magnetic field is applied. Our model consists of two parts: a Monte Carlo simulation of the dynamics of carriers generated by a subpicosecond optical pulse, and a calculation of the resulting THz radiation emitted through the semiconductor surface. The magnetic field deflects the motion of the carriers, producing a component of the THz dipole parallel to the surface. This causes the power transmitted through the surface to be increased by more than one order of magnitude.
Publisher: IEEE
Date: 2002
Publisher: IEEE
Date: 06-2012
Publisher: AIP
Date: 2013
DOI: 10.1063/1.4848506
Publisher: American Chemical Society (ACS)
Date: 04-02-2021
Publisher: Springer Science and Business Media LLC
Date: 20-12-2021
DOI: 10.1038/S41377-021-00685-5
Abstract: The exploitation of ultrafast electron dynamics in quantum cascade lasers (QCLs) holds enormous potential for intense, compact mode-locked terahertz (THz) sources, squeezed THz light, frequency mixers, and comb-based metrology systems. Yet the important sub-cycle dynamics have been notoriously difficult to access in operational THz QCLs. Here, we employ high-field THz pulses to perform the first ultrafast two-dimensional spectroscopy of a free-running THz QCL. Strong incoherent and coherent nonlinearities up to eight-wave mixing are detected below and above the laser threshold. These data not only reveal extremely short gain recovery times of 2 ps at the laser threshold, they also reflect the nonlinear polarization dynamics of the QCL laser transition for the first time, where we quantify the corresponding dephasing times between 0.9 and 1.5 ps with increasing bias currents. A density-matrix approach reproducing the emergence of all nonlinearities and their ultrafast evolution, simultaneously, allows us to map the coherently induced trajectory of the Bloch vector. The observed high-order multi-wave mixing nonlinearities benefit from resonant enhancement in the absence of absorption losses and bear potential for a number of future applications, ranging from efficient intracavity frequency conversion, mode proliferation to passive mode locking.
Publisher: IEEE
Date: 09-2013
Publisher: IOP Publishing
Date: 07-1993
Publisher: IEEE
Date: 09-2012
Publisher: Springer Science and Business Media LLC
Date: 27-08-2020
DOI: 10.1038/S41467-020-18004-8
Abstract: Semiconductor heterostructures have enabled a great variety of applications ranging from GHz electronics to photonic quantum devices. While nonlinearities play a central role for cutting-edge functionality, they require strong field litudes owing to the weak light-matter coupling of electronic resonances of naturally occurring materials. Here, we ultrastrongly couple intersubband transitions of semiconductor quantum wells to the photonic mode of a metallic cavity in order to custom-tailor the population and polarization dynamics of intersubband cavity polaritons in the saturation regime. Two-dimensional THz spectroscopy reveals strong subcycle nonlinearities including six-wave mixing and a collapse of light-matter coupling within 900 fs. This collapse bleaches the absorption, at a peak intensity one order of magnitude lower than previous all-integrated approaches and well achievable by state-of-the-art QCLs, as demonstrated by a saturation of the structure under cw-excitation. We complement our data by a quantitative theory. Our results highlight a path towards passively mode-locked QCLs based on polaritonic saturable absorbers in a monolithic single-chip design.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 04-10-2019
Abstract: We bring to light the complex interplay of optical nonlinearities in quantum structures.
Publisher: American Chemical Society (ACS)
Date: 07-2020
Publisher: Optica Publishing Group
Date: 24-03-2009
DOI: 10.1364/OL.34.001030
Abstract: We report the generation of Bessel beams using polytetrafluoroethene conical lenses and a quantum cascade laser emitting at 2.8 THz. The formation of a central beam spot that retains its size over distances exceeding the characteristic Rayleigh range is demonstrated, and the power transport properties of these beams are compared with those obtained using parabolic reflectors. These lenses could provide an attractive alternative to parabolic reflectors for terahertz imaging applications where a large depth of focus and/or efficient and controllable coupling of radiation onto a small target are desirable.
Publisher: SPIE
Date: 29-11-2007
DOI: 10.1117/12.785002
Publisher: IEEE
Date: 09-2019
Publisher: The Optical Society
Date: 29-08-2016
DOI: 10.1364/OE.24.020554
Publisher: IEEE
Date: 12-2014
Publisher: IEEE
Date: 08-2017
Publisher: Springer Science and Business Media LLC
Date: 2009
DOI: 10.1038/NATURE07636
Abstract: Semiconductor lasers based on two-dimensional photonic crystals generally rely on an optically pumped central area, surrounded by un-pumped, and therefore absorbing, regions. This ideal configuration is lost when photonic-crystal lasers are electrically pumped, which is practically more attractive as an external laser source is not required. In this case, in order to avoid lateral spreading of the electrical current, the device active area must be physically defined by appropriate semiconductor processing. This creates an abrupt change in the complex dielectric constant at the device boundaries, especially in the case of lasers operating in the far-infrared, where the large emission wavelengths impose device thicknesses of several micrometres. Here we show that such abrupt boundary conditions can dramatically influence the operation of electrically pumped photonic-crystal lasers. By demonstrating a general technique to implement reflecting or absorbing boundaries, we produce evidence that whispering-gallery-like modes or true photonic-crystal states can be alternatively excited. We illustrate the power of this technique by fabricating photonic-crystal terahertz (THz) semiconductor lasers, where the photonic crystal is implemented via the sole patterning of the device top metallization. Single-mode laser action is obtained in the 2.55-2.88 THz range, and the emission far field exhibits a small angular ergence, thus providing a solution for the quasi-total lack of directionality typical of THz semiconductor lasers based on metal-metal waveguides.
Publisher: The Optical Society
Date: 30-01-2015
DOI: 10.1364/OE.23.002720
Publisher: The Optical Society
Date: 09-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B817839A
Abstract: Terahertz frequency time-domain spectroscopy has been used to analyse a wide range of s les containing cocaine hydrochloride, heroin and ecstasy--common drugs-of-abuse. We investigated real-world s les seized by law enforcement agencies, together with pure drugs-of-abuse, and pure drugs-of-abuse systematically adulterated in the laboratory to emulate real-world s les. In order to investigate the feasibility of automatic spectral recognition of such illicit materials by terahertz spectroscopy, principal component analysis was employed to cluster spectra of similar compounds.
Publisher: American Physical Society (APS)
Date: 29-06-2001
Publisher: IEEE
Date: 10-2013
Publisher: AIP Publishing
Date: 22-06-2009
DOI: 10.1063/1.3158592
Publisher: Springer Netherlands
Date: 2007
Publisher: American Physical Society (APS)
Date: 19-09-2017
Publisher: AIP Publishing
Date: 03-06-2013
DOI: 10.1063/1.4808385
Abstract: We demonstrate the generation of high order terahertz (THz) frequency sidebands (up to 3rd order) on a near infrared (NIR) optical carrier within a THz quantum cascade laser (QCL). The NIR carrier is resonant with the interband transition of the quantum wells composing the QCL, allowing the nonlinearity to be enhanced and leading to frequency mixing. A phonon depopulation based QCL with a double metal cavity was used to enhance the intracavity power density and to demonstrate the higher order sidebands. The 1st order sideband intensity shows a linear dependence with THz power corresponding to a single THz photon, while the second order sideband has a quadratic dependence implying a two THz photon interaction and hence a third order susceptibility. These measurements are compared to the photoluminescence and the QCL bandstructure to identify the states involved, with the lowest conduction band states contributing the most to the sideband intensity. We also show that the interaction for the second order sideband corresponds to an enhanced direct third order susceptibility χ(3) of ∼7 × 10−16(m/V)2, two orders of magnitude greater than the bulk value.
Publisher: Elsevier BV
Date: 2002
Publisher: IEEE
Date: 08-2017
Publisher: American Physical Society (APS)
Date: 12-09-2022
Publisher: AIP Publishing
Date: 27-07-2020
DOI: 10.1063/5.0014251
Abstract: Photonic engineering of the terahertz emission from a quantum cascade laser (QCL) is fundamental for the exploitation of this unique source in a myriad of applications where it can be implemented, such as spectroscopy, imaging, and sensing. Active control of the frequency, power, polarization, and beam profile has been achieved through a variety of approaches. In particular, the active control of the emitted frequency, which is difficult to determine a priori, has been achieved through the integration of a photonic structure and/or by using external cavity arrangements. In this work, an external cavity arrangement, which implements a metamaterial/graphene optoelectronic mirror as an external feedback element, is proposed and demonstrated. The reflectivity and dispersion properties of the external active mirror were tuned via electrostatically gating graphene. It was possible to electronically reproduce the mode-switch occurring in a QCL emitting ∼2.8 THz by mechanically changing the external cavity length formed by an Au mirror. The external cavity arrangement was investigated and described in the framework of the self-mixing theory. These results open a way for the all-electronic engineering of the QCL emission by the use of a fast reconfigurable external mirror. This approach can uniquely address both power and frequency control, with ∼100 MHz reconfiguration speeds, using an integrated external element. Furthermore, the metamaterial/graphene mirror's strong dispersive properties might be implemented for the active mode locking of THz QCLs. Finally, this approach offers a unique opportunity to study the laser dynamics and mode competition in THz QCLs in the self-mixing feedback regime.
Publisher: IOP Publishing
Date: 14-03-2019
Publisher: The Royal Society
Date: 17-12-2003
Publisher: Elsevier BV
Date: 07-2003
Publisher: AIP Publishing
Date: 08-09-2020
DOI: 10.1063/5.0018865
Abstract: Scanning-probe-assisted mid-infrared nano-spectroscopy is employed to reveal the polaritonic dispersion of in idual MIM (metal-insulator-metal) square patch antennas whose modes can be strongly coupled to a mid-infrared intersubband transition. The patch antenna side length L sets the resonances between λ = 5.5 μm and 12.5 μm. The active region consists of a highly doped AlInAs/InGaAs/AlInAs single quantum well that presents an intersubband transition at 1190 cm−1 (λ = 8.4 μm). When the patch antenna optical resonance approaches and matches the intersubband transition frequency (L ∼ 1.8 μm), a clear anticrossing behavior—evidence of strong coupling—is observed in the near-field scattering phase spectra of in idual antennas. The measured Rabi splitting is 4.5 THz. The near-field scattering spectra agree with the far-field extinction spectra acquired on arrays of identical antennas.
Publisher: IEEE
Date: 10-2011
Publisher: IEEE
Date: 2001
Publisher: Optica Publishing Group
Date: 15-08-2022
DOI: 10.1364/OE.467673
Abstract: Lasers that can emit two photons from a single electron relaxation between two states of the same parity have been discussed since the early days of the laser era. However, such lasers have seen only limited success, mainly due to a lack of suitable gain medium. We propose that terahertz (THz) frequency quantum cascade lasers (QCLs) are an ideal semiconductor structure to realize such two-photon emissions. In this work, we present a THz QCL heterostructure designed to emit two resonant photons from each electronic relaxation between two same-parity states in the active region. We present coupled Maxwell-Bloch equations that describe the dynamics of such a two-photon laser and find analytical solutions for the steady-state light intensity, the steady-state energy-resolved carrier densities, and the total threshold carrier density. Due to the two-photon emission from each excited state relaxation and an increased photon-driven carrier transport rate, our simulations predict a significant enhancement of light intensity in our designed resonant two-photon THz QCL when compared to an exemplar conventional THz QCL structure.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2005
Publisher: IEEE
Date: 09-2013
Publisher: Springer Science and Business Media LLC
Date: 15-06-2017
DOI: 10.1038/NCOMMS15763
Abstract: Saturable absorbers (SA) operating at terahertz (THz) frequencies can open new frontiers in the development of passively mode-locked THz micro-sources. Here we report the fabrication of THz SAs by transfer coating and inkjet printing single and few-layer graphene films prepared by liquid phase exfoliation of graphite. Open-aperture z -scan measurements with a 3.5 THz quantum cascade laser show a transparency modulation ∼80%, almost one order of magnitude larger than that reported to date at THz frequencies. Fourier-transform infrared spectroscopy provides evidence of intraband-controlled absorption bleaching. These results pave the way to the integration of graphene-based SA with electrically pumped THz semiconductor micro-sources, with prospects for applications where excitation of specific transitions on short time scales is essential, such as time-of-flight tomography, coherent manipulation of quantum systems, time-resolved spectroscopy of gases, complex molecules and cold s les and ultra-high speed communications, providing unprecedented compactness and resolution.
Publisher: IEEE
Date: 09-2006
Publisher: AIP Publishing
Date: 15-09-2006
DOI: 10.1063/1.2335601
Abstract: We report on a numerical study of the sensitivity of electrical terahertz (THz) frequency range passive filters under conditions of dielectric loading. We investigate band-pass filters, ring resonators, and band-stop filters, all of which have been proposed as devices capable of measuring the hybridization state of overlaid DNA films, thereby acting as genetic sensors. The transmission characteristics of these filters are examined when loaded with s les of different relative permittivities and thicknesses, and these results are discussed in the context of recent experimental works. A comparative analysis of the three filter types is performed, and conclusions are drawn on the suitability of the various filters for the analysis of DNA films during genetic testing and other dielectric materials.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2009
Publisher: AIP Publishing
Date: 28-01-2008
DOI: 10.1063/1.2838748
Abstract: We report on the use of standing surface acoustic waves, formed on a single-crystal piezoelectric substrate, to organize micron-scale latex particles into an array comprising a series of lines in an adjacent microfluidic system. The lines of particles are formed parallel to the substrate surface and perpendicular to the surface acoustic wave vector. They extend across the width of the acoustic beam aperture, with a periodicity of one-half the surface acoustic wavelength. The position and spacing of the particle arrays can be altered by adjusting the acoustic wave frequency within the device passband. We discuss the mechanism responsible for the formation of the lines, which could be widely applicable to the alignment of microscopic objects held in suspension.
Publisher: IOP Publishing
Date: 21-06-2007
Publisher: AIP Publishing
Date: 07-12-2009
DOI: 10.1063/1.3271030
Abstract: We report the development of a terahertz pulsed spectroscopic imaging system based on the concept of compressive sensing. A single-point terahertz detector, together with a set of 40 optimized two-dimensional binary masks, was used to measure the terahertz waveforms transmitted through a s le. Terahertz time- and frequency-domain images of the s le comprising 20×20 pixels were subsequently reconstructed. We demonstrate that both the spatial distribution and the spectral characteristics of a s le can be obtained by this means. Compared with conventional terahertz pulsed imaging, no raster scanning of the object is required, and ten times fewer terahertz spectra need be taken. It is therefore ideal for real-time imaging applications.
Publisher: OSA
Date: 2014
Publisher: IOP Publishing
Date: 05-08-2013
Publisher: AIP Publishing
Date: 21-01-2008
DOI: 10.1063/1.2835202
Abstract: Terahertz quantum cascade lasers with wide-ridge metal-metal waveguides are prone to lasing in high-order lateral modes, which reduce the maximum light output power from these devices. We have demonstrated, theoretically and experimentally, that the output power can be improved severalfold by introducing “side absorbers” into the waveguide structure, which enforce lasing in the TM00 mode with minor temperature performance deterioration. Lasers without side absorbers operate up to 168K, a current record for devices processed using indium/gold wafer bonding.
Publisher: Elsevier BV
Date: 03-2004
Publisher: IEEE
Date: 09-2014
Publisher: American Chemical Society (ACS)
Date: 19-06-2018
Publisher: AIP Publishing
Date: 09-08-2002
DOI: 10.1063/1.1498861
Abstract: A quantum-cascade laser operating at λ=66 μm is demonstrated. It consists of a three-quantum-well chirped-superlattice active region embedded in a waveguide based on a single interface plasmon and a buried contact. A threshold current density of 210 A/cm2 at T=12 K, a maximum peak optical power of 4 mW, and operation up to T=44 K are achieved in a 2.7 mm long device with a high reflectivity backfacet coating.
Publisher: The Optical Society
Date: 28-03-2019
DOI: 10.1364/OE.27.010221
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2019
Publisher: SPIE
Date: 09-02-2006
DOI: 10.1117/12.660716
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2013
Publisher: IEEE
Date: 09-2006
Publisher: IEEE
Date: 10-2012
Publisher: Springer Science and Business Media LLC
Date: 24-04-2020
DOI: 10.1038/S42005-020-0344-0
Abstract: Four-wave-mixing-based quantum cascade laser frequency combs (QCL-FC) are a powerful photonic tool, driving a recent revolution in major molecular fingerprint regions, i.e. mid- and far-infrared domains. Their compact and frequency-agile design, together with their high optical power and spectral purity, promise to deliver an all-in-one source for the most challenging spectroscopic applications. Here, we demonstrate a metrological-grade hybrid dual comb spectrometer, combining the advantages of a THz QCL-FC with the accuracy and absolute frequency referencing provided by a free-standing, optically-rectified THz frequency comb. A proof-of-principle application to methanol molecular transitions is presented. The multi-heterodyne molecular spectra retrieved provide state-of-the-art results in line-center determination, achieving the same precision as currently available molecular databases. The devised setup provides a solid platform for a new generation of THz spectrometers, paving the way to more refined and sophisticated systems exploiting full phase control of QCL-FCs, or Doppler-free spectroscopic schemes.
Publisher: Springer Science and Business Media LLC
Date: 23-01-2017
DOI: 10.1038/SREP41081
Abstract: The use of DNA as a structural material for nanometre-scale construction has grown extensively over the last decades. The development of more advanced DNA-based materials would benefit from a modular approach enabling the direct assembly of additional elements onto nanostructures after fabrication. RecA-based nucleoprotein filaments encapsulating short ssDNA have been demonstrated as a tool for highly efficient and fully programmable post-hoc patterning of duplex DNA scaffold. However, the underlying assembly process is not fully understood, in particular when patterning complex DNA topologies. Here, we report the effect of basepair-mismatched regions and single-strand nicks in the double-stranded DNA scaffold on the yield of RecA-based assembly. Significant increases in assembly yield are observed upon the introduction of unpaired basepairs directly adjacent to the assembly region. However, when the unpaired regions were introduced further from the assembly site the assembly yield initially decreased as the length of the unpaired region was increased. These results suggest that an unpaired region acts as a kinetic trap for RecA-based nucleoprotein filaments, impeding the assembly mechanism. Conversely, when the unpaired region is located directly adjacent to the assembly site, it leads to an increase in efficiency of RecA patterning owing to increased breathing of the assembly site.
Publisher: IOP Publishing
Date: 2001
Publisher: IOP Publishing
Date: 05-04-2023
Abstract: Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.
Publisher: American Chemical Society (ACS)
Date: 24-01-2003
DOI: 10.1021/LA026513W
Publisher: The Optical Society
Date: 25-01-2019
DOI: 10.1364/OE.27.002248
Publisher: AIP Publishing
Date: 03-10-2016
DOI: 10.1063/1.4963891
Abstract: We study the emission properties of an electroluminescent THz frequency quantum cascade structure embedded in an array of patch antenna double-metal microcavities. We show that high photon extraction efficiencies can be obtained by adjusting the active region thickness and array periodicity as well as high Purcell factors (up to 65), leading to an enhanced overall emitted power. Up to a 44-fold increase in power is experimentally observed in comparison with a reference device processed in conventional mesa geometry. Estimation of the Purcell factors using electromagnetic simulations and the theoretical extraction efficiency are in agreement with the observed power enhancement and show that, in these microcavities, the overall enhancement solely depends on the square of the total quality factor.
Publisher: IEEE
Date: 2002
Publisher: American Chemical Society (ACS)
Date: 13-06-2018
Publisher: Elsevier BV
Date: 06-2016
Publisher: The Optical Society
Date: 09-07-2012
DOI: 10.1364/OE.20.016662
Publisher: Informa UK Limited
Date: 07-2006
Publisher: American Chemical Society (ACS)
Date: 06-08-2013
DOI: 10.1021/AC401657R
Abstract: The absorption coefficient and refractive index have been measured for a homologous series of tetraalkylammonium bromides over the frequency range 0.3-5.5 THz. Spectral features are found to shift to lower frequencies as the molecular mass is increased, as expected. However, to understand the detailed structure of the observed spectral features, density functional perturbation theory calculations have been performed on the first four crystalline compounds in the series. From these calculations, we find that each spectrum is dominated by three translatory modes involving asymmetric motion of the ammonium cation and bromine counterion, although the overall number of active modes increases with increasing molecular size. The experimentally observed absorption is not completely described by the infrared active phonon modes alone. We show that it is also necessary to include the coupling of the phonon modes with the macroscopic field generated by the collective displacement of the vibrating ions, and we have applied an effective medium theory, which accounts for particle shape to allow for this effect in the calculation of the terahertz spectra.
Publisher: American Physical Society (APS)
Date: 15-09-1992
Publisher: Elsevier BV
Date: 02-1992
Publisher: AIP Publishing
Date: 17-05-2005
DOI: 10.1063/1.1938255
Abstract: We report the operation of band-stop filters in the terahertz (THz) frequency range, working at a center frequency of 600GHz. The filters were characterized by embedding them in a microstrip line attached to photoconductive switches which act as THz emitters and detectors. The filters have applications in sensing and detection. The chosen filter design allows cascading of several filters along the same microstrip line, which is of particular importance for a proposed molecular sensing array.
Publisher: Institution of Engineering and Technology (IET)
Date: 10-2018
DOI: 10.1049/EL.2018.6062
Publisher: Springer Science and Business Media LLC
Date: 19-12-2014
DOI: 10.1038/NCOMMS6884
Abstract: Quasi-crystal structures do not present a full spatial periodicity but are nevertheless constructed starting from deterministic generation rules. When made of different dielectric materials, they often possess fascinating optical properties, which lie between those of periodic photonic crystals and those of a random arrangement of scatterers. Indeed, they can support extended band-like states with pseudogaps in the energy spectrum, but lacking translational invariance, they also intrinsically feature a pattern of ‘defects’, which can give rise to critically localized modes confined in space, similar to Anderson modes in random structures. If used as laser resonators, photonic quasi-crystals open up design possibilities that are simply not possible in a conventional periodic photonic crystal. In this letter, we exploit the concept of a 2D photonic quasi crystal in an electrically injected laser specifically, we pattern the top surface of a terahertz quantum-cascade laser with a Penrose tiling of pentagonal rotational symmetry, reaching 0.1–0.2% wall-plug efficiencies and 65 mW peak output powers with characteristic surface-emitting conical beam profiles, result of the rich quasi-crystal Fourier spectrum.
Publisher: SPIE
Date: 28-09-2200
DOI: 10.1117/12.689389
Publisher: IEEE
Date: 2001
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2016
Publisher: AIP Publishing
Date: 20-04-2015
DOI: 10.1063/1.4918993
Abstract: Terahertz-frequency quantum cascade lasers (THz QCLs) based on bound-to-continuum active regions are difficult to model owing to their large number of quantum states. We present a computationally efficient reduced rate equation (RE) model that reproduces the experimentally observed variation of THz power with respect to drive current and heat-sink temperature. We also present dynamic (time-domain) simulations under a range of drive currents and predict an increase in modulation bandwidth as the current approaches the peak of the light–current curve, as observed experimentally in mid-infrared QCLs. We account for temperature and bias dependence of the carrier lifetimes, gain, and injection efficiency, calculated from a full rate equation model. The temperature dependence of the simulated threshold current, emitted power, and cut-off current are thus all reproduced accurately with only one fitting parameter, the interface roughness, in the full REs. We propose that the model could therefore be used for rapid dynamical simulation of QCL designs.
Publisher: IEEE
Date: 05-2013
Publisher: IOP Publishing
Date: 16-11-2012
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3LC50485A
Abstract: We investigate the effect of substrate thickness on the transmission bandwidth of on-chip terahertz-frequency-range planar Goubau lines both experimentally and theoretically. The bandwidth and frequency resolution are improved through substrate thinning and geometry modifications (reducing reflections arising from the THz photoconductive generators and detectors). We demonstrate that the enhanced bandwidth (2 THz) and resolution (3.75 GHz) allows this type of on-chip waveguide to be used for spectroscopic measurements of polycrystalline materials from cryogenic (4 K) to room temperature (292 K) by recording vibrational absorption spectra from overlaid s les of lactose monohydrate.
Publisher: AIP Publishing
Date: 05-12-2016
DOI: 10.1063/1.4969067
Abstract: We report on the realization of a monolithically integrated master-oscillator power- lifier architecture in a terahertz quantum cascade laser (THz-QCL) with a metal-metal waveguide. The master-oscillator section is a first-order distributed feedback (DFB) laser. Instead of using a thick anti-reflection coating, we exploit a diffraction grating together with an absorbing boundary in the power- lifier section to efficiently extract the laser radiation and suppress the self-lasing in it. The devices demonstrate a stable generation and power lification of single-mode emission. The lification factor is about 5, and the output power is approximately twice that of the standard second-order DFB lasers fabricated from the same material. Emission beam pattern with a ergence angle of ∼18 × 40° is achieved. Our work provides an avenue for the realization of single-mode THz-QCLs with high output power and good beam quality.
Publisher: The Optical Society
Date: 20-02-2015
DOI: 10.1364/OE.23.005190
Publisher: The Optical Society
Date: 15-02-2012
DOI: 10.1364/OL.37.000731
Publisher: American Physical Society (APS)
Date: 15-03-1999
Publisher: Springer Science and Business Media LLC
Date: 12-06-2023
DOI: 10.1038/S41377-023-01200-8
Abstract: One of the most exciting breakthroughs in physics is the concept of topology that was recently introduced to photonics, achieving robust functionalities, as manifested in the recently demonstrated topological lasers. However, so far almost all attention was focused on lasing from topological edge states. Bulk bands that reflect the topological bulk-edge correspondence have been largely missed. Here, we demonstrate an electrically pumped topological bulk quantum cascade laser (QCL) operating in the terahertz (THz) frequency range. In addition to the band-inversion induced in-plane reflection due to topological nontrivial cavity surrounded by a trivial domain, we further illustrate the band edges of such topological bulk lasers are recognized as the bound states in the continuum (BICs) due to their nonradiative characteristics and robust topological polarization charges in the momentum space. Therefore, the lasing modes show both in-plane and out-of-plane tight confinements in a compact laser cavity (lateral size ~3λ laser ). Experimentally, we realize a miniaturized THz QCL that shows single-mode lasing with a side-mode suppression ratio (SMSR) around 20 dB. We also observe a cylindrical vector beam for the far-field emission, which is evidence for topological bulk BIC lasers. Our demonstration on miniaturization of single-mode beam-engineered THz lasers is promising for many applications including imaging, sensing, and communications.
Publisher: AIP Publishing
Date: 28-12-2015
DOI: 10.1063/1.4938207
Abstract: Tunable oscillators are a key component of almost all electronic and photonic systems. Yet, a technology capable of operating in the terahertz (THz)-frequency range and fully suitable for widescale implementation is still lacking. This issue is significantly limiting potential THz applications in gas sensing, high-resolution spectroscopy, hyper-spectral imaging, and optical communications. The THz quantum cascade laser is arguably the most promising solution in terms of output power and spectral purity. In order to achieve reliable, repeatable, and broad tunability, here we exploit the strong coupling between two different cavity mode concepts: a distributed feedback one-dimensional photonic resonator (providing gain) and a mechanically actuated wavelength-size microcavity (providing tuning). The result is a continuously tunable, single-mode emitter covering a 162 GHz spectral range, centered on 3.2 THz. Our source has a few tens of MHz resolution, extremely high differential efficiency, and unprecedented compact and simple design architecture. By unveiling the large potential that lies in this technique, our results provide a robust platform for radically different THz systems exploiting broadly tunable semiconductor lasers.
Publisher: American Chemical Society (ACS)
Date: 31-12-2018
Publisher: Optica Publishing Group
Date: 05-07-2023
DOI: 10.1364/OE.490217
Abstract: The response of terahertz to the presence of water content makes it an ideal analytical tool for hydration monitoring in agricultural applications. This study reports on the feasibility of terahertz sensing for monitoring the hydration level of freshly harvested leaves of Celtis sinensis by employing a imaging platform based on quantum cascade lasers and laser feedback interferometry. The imaging platform produces wide angle high resolution terahertz litude and phase images of the leaves at high frame rates allowing monitoring of dynamic water transport and other changes across the whole leaf. The complementary information in the resulting images was fed to a machine learning model aiming to predict relative water content from a single frame. The model was used to predict the change in hydration level over time. Results of the study suggest that the technique could have substantial potential in agricultural applications.
Publisher: IEEE
Date: 2002
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2015
Publisher: Elsevier BV
Date: 06-1998
Publisher: SPIE
Date: 10-02-2011
DOI: 10.1117/12.870833
Publisher: Elsevier BV
Date: 03-2002
Publisher: The Optical Society
Date: 12-2016
DOI: 10.1364/OE.24.028583
Publisher: AIP Publishing
Date: 20-04-2015
DOI: 10.1063/1.4918983
Abstract: We report on the implementation of 5 THz quantum well photodetector exploiting a patch antenna cavity array. The benefit of our plasmonic architecture on the detector performance is assessed by comparing it with detectors made using the same quantum well absorbing region, but processed into a standard 45° polished facet mesa. Our results demonstrate a clear improvement in responsivity, polarization insensitivity, and background limited performance. Peak detectivities in excess of 5 × 1012 cmHz1/2/W have been obtained, a value comparable with that of the best cryogenic cooled bolometers.
Publisher: AIP Publishing
Date: 17-06-2004
DOI: 10.1063/1.1767957
Abstract: Distributed feedback terahertz quantum-cascade lasers emitting at 4.34 and 4.43THz are presented. Mode selection is based on a complex-coupling scheme implemented into the top-contact layer by a combination of wet chemical etching and ohmic-contact deposition. Single-mode emission stable at all injection currents and operating temperatures is shown, with a side-mode suppression ratio exceeding 20dB. Peak output powers of up to 1.8mW are obtained at low temperatures.
Publisher: American Physical Society (APS)
Date: 08-03-2021
Publisher: The Optical Society
Date: 12-09-2016
DOI: 10.1364/OE.24.021948
Publisher: IEEE
Date: 09-2019
Publisher: Springer Science and Business Media LLC
Date: 2003
Publisher: American Chemical Society (ACS)
Date: 03-12-2020
Publisher: SPIE
Date: 08-04-2004
DOI: 10.1117/12.542788
Publisher: American Scientific Publishers
Date: 12-2011
Abstract: Molecular lock-and-key functionality inherent to a large number of biological molecules is arguably one of the most promising potential routes for building complex nanostructures and eventually nano-electronic devices by self-assembly. Here, we report the use of the DNA-binding protein RecA as a tool for patterning DNA scaffolds site-specifically and in a programmable way at the nanometre-scale. This is demonstrated by patterning a 3 kilo-base-pair double-stranded DNA molecule at ten different locations with nanometre-sized RecA-based nucleoprotein filaments. This protein-based molecular patterning technique, which is site-specific, programmable, and scalable, offers a potential basis for molecular lithography applications, and opens previously inaccessible routes towards the fabrication of complex functional nano-electronic devices by self-assembly.
Publisher: AIP Publishing
Date: 21-03-2013
DOI: 10.1063/1.4795606
Abstract: We report three-well, resonant-phonon depopulation terahertz quantum cascade lasers with semi-insulating surface-plasmon waveguides and reduced active region (AR) thicknesses. Devices with thicknesses of 10, 7.5, 6, and 5 μm are compared in terms of threshold current density, maximum operating temperature, output power, and AR temperature. Thinner ARs are technologically less demanding for epitaxial growth and result in reduced electrical heating of devices. However, it is found that 7.5-μm-thick devices give the lowest electrical power densities at threshold, as they represent the optimal trade-off between low electrical resistance and low threshold gain.
Publisher: AIP Publishing
Date: 11-04-2011
DOI: 10.1063/1.3579258
Abstract: We report a polarization-sensitive terahertz time-domain spectroscopy system, which allows the simultaneous measurement of orthogonal components of the polarization of a free-space propagating terahertz beam using a dual electro-optic detection scheme. We demonstrate the operation of our system by measuring the birefringence of lithium niobate, simultaneously obtaining terahertz spectra from two orthogonal crystallographic directions.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2020
Publisher: Springer Science and Business Media LLC
Date: 06-01-2016
Publisher: Wiley
Date: 10-01-2012
Publisher: IEEE
Date: 10-2011
Publisher: IEEE
Date: 09-2013
Publisher: The Optical Society
Date: 04-12-2018
DOI: 10.1364/OL.43.005933
Publisher: The Optical Society
Date: 12-09-2013
DOI: 10.1364/OE.21.022194
Publisher: AIP Publishing
Date: 16-12-2004
DOI: 10.1063/1.1825627
Abstract: The authors investigate the elongation and orientation of different-sized deoxyribose nucleic acid (DNA) molecules, tethered onto gold electrodes via a terminal thiol, under the influence of high frequency ac electric fields. The DNA molecules are elongated from a random coil into an extended conformation and orientated along the electric field lines as a result of the forces acting on the molecules during the application of the ac electric fields. Elongation was observed in the frequency range 100kHz–1MHz, with field strengths of 0.06–1.0MV∕m. Maximum elongation for all DNA fragments tested, irrespective of size, was found for frequencies between 200 and 300kHz. The torque acting on the induced dipole in the DNA molecules, complemented by a directional bias force, opposite in direction to the dielectrophoretic force, provides the main contribution to the elongation process. The length of elongation is limited to either half the distance between opposing electrodes or to the contour length of the DNA, whichever is shorter. Further, the authors show that the normalized length of the elongated DNA molecules is independent of the contour length of the DNA.
Publisher: AIP Publishing
Date: 05-08-2003
DOI: 10.1063/1.1597985
Abstract: We present a study of far-infrared intersubband electroluminescence from a number of GaAs–Al0.15Ga0.85As quantum-cascade emitters with emission energies below the LO phonon energy. A range of s les with emission energies between 13 and 21 meV were investigated. A systematic decrease in the normalized emission intensity with increasing intersubband separation was observed. The possible mechanisms such as the grating coupling efficiency and the role of scattering processes are discussed.
Publisher: American Chemical Society (ACS)
Date: 07-01-2011
DOI: 10.1021/LA103733J
Abstract: The structural stability of alkenthiolate monolayers assembled on gold surfaces is a result of the well-defined organization of the in idual molecules within the film. The formation of three-dimensional films assembled by stacking multiple molecular monolayers is substantially more challenging because the correct organization of the molecular components is required not only within the in idual monolayers but also between the monolayers of the film. In this paper we examine the structure of multilayer films based on mercaptoalkanoic acid monolayers in which ligation between adjacent monolayers is achieved using the interaction of carboxylic acid and thiol groups with a alent Cu ion. Using contact angle analysis and atomic force microscopy, we show that the use of Cu(2+) has profound implications on the properties and structure of the multilayer film. In particular, the alent ions effectively prohibit the complete assembly of the next monolayer. For multilayer SAMs assembled from short alkane chains with six methylene groups, we find that molecules in the incomplete adlayer organize themselves randomly over the underlying monolayer. However, as the number of methylene groups increases (11 and 16 methylene groups), the upper layer tends to fracture into discrete islands which cover around 50% of the surface. The height of these islands is found to be equal to that expected for a complete, well-ordered monolayer assembled from the equivalent mercaptoalkanoic acid molecules. This relationship between chain length and island growth results from the migration of molecules into ordered aggregates driven by the reduction of free energy associated with maximizing intermolecular interactions.
Publisher: AIP Publishing
Date: 28-10-2013
DOI: 10.1063/1.4827886
Abstract: We demonstrate coherent terahertz (THz) frequency imaging using the self-mixing effect in a quantum cascade laser (QCL). Self-mixing voltage waveforms are acquired at each pixel of a two-dimensional image of etched GaAs structures and fitted to a three-mirror laser model, enabling extraction of the litude and phase parameters of the reflected field. From the phase, we reconstruct the depth of the s le surface, and we show that the litude can be related to the s le reflectance. Our approach is experimentally simple and compact, and does not require frequency stabilization of the THz QCL.
Publisher: Elsevier BV
Date: 06-1998
Publisher: Optica Publishing Group
Date: 16-11-2021
DOI: 10.1364/OE.437861
Abstract: In this article, we explore the interplay between the self-pulsations (SPs) and self-mixing (SM) signals generated in terahertz (THz) quantum cascade lasers (QCLs) under optical feedback. We find that optical feedback dynamics in a THz QCL, namely, SPs, modulate the conventional SM interference fringes in a laser feedback interferometry system. The phenomenon of fringe loss in the SM signal — well known in interband diode lasers — was also observed along with pronounced SPs. With an increasing optical feedback strength, SM interference fringes transition from regular fringes at weak feedback ( C ≤ 1) to fringes modulated by SPs under moderate feedback (1 C ≤ 4.6), and then [under strong feedback ( C 4.6)] to a SM waveform with reduced number of fringes modulated by SP, until eventually (under even greater feedback) all the fringes are lost and only SPs are left visible. The transition route described above was identified in simulation when the SM fringes are created either by a moving target or a current modulation of the THz QCL. This SM signal transition route was successfully validated experimentally in a pulsed mode THz QCL with SM fringes created by current modulation during the pulse. The effects of SP dynamics in laser feedback interferometric system investigated in this work not only provides a further understanding of nonlinear dynamics in a THz QCL but also helps to understand the SM waveforms generated in a THz QCLs when they are used for various sensing and imaging applications.
Publisher: IEEE
Date: 09-2014
Publisher: AIP Publishing
Date: 15-10-2018
DOI: 10.1063/1.5051580
Abstract: Current noise fluctuations have been investigated in terahertz (THz) quantum well photodetectors embedded in antenna-coupled photonic architectures and compared with standard substrate-coupled mesa detectors. The noise measurements give a value of the photoconductive gain that is in excellent agreement with that extracted from previous responsivity calibrations. Moreover, our results confirm that the noise equivalent power (NEP) of the antenna-coupled devices is of the order of 0.2 pW/Hz0.5. This low NEP value and the wide band frequency response (∼GHz) of the detectors are ideal figures for the development of heterodyne receivers that are, at present, a valuable technological solution to overcome the current limitation of THz sensors.
Publisher: IOP Publishing
Date: 28-08-2014
Publisher: AIP Publishing
Date: 05-2012
DOI: 10.1063/1.4711101
Abstract: We demonstrate that aqueous suspensions of microbubbles, formed into arrays using standing surface acoustic waves (SSAWs), can be transported by controlled modulation of the SSAW frequency. The array is repeatedly captured at a sequence of spatial positions along the acoustic beam path and long-range transportation is achieved by periodic cycling of the applied frequency across the transducer bandwidth. We also demonstrate that controllable alignment and transport can be achieved in a detachable microfluidic device, where the microfluidic channel, in which particle transport occurs, is separated from the piezoelectric substrate by an acoustic coupling gel. Proof-of-concept transport is first discussed using a test system of latex particles before the non-invasive manipulation technique is applied to arrays of microbubbles. We explore the role of acoustic radiation forces in the spatial control of particles by analysing the dynamics of particle manipulation by SSAWs. Our results highlight the exquisite control which we have over the position and transport of particles and we anticipate that this technique could find wide applications for the accurate and programmable, non-invasive ordering and transport of biological s les in microfluidic systems.
Publisher: AIP Publishing
Date: 05-01-2015
DOI: 10.1063/1.4905338
Abstract: We have developed terahertz frequency quantum cascade lasers that exploit a double-periodicity distributed feedback grating to control the emission frequency and the output beam direction independently. The spatial refractive index modulation of the gratings necessary to provide optical feedback at a fixed frequency, and simultaneously, a far-field emission pattern centered at controlled angles, was designed through use of an appropriate wavevector scattering model. Single mode terahertz (THz) emission at angles tuned by design between 0° and 50° was realized, leading to an original phase-matching approach for highly collimated THz quantum cascade lasers.
Publisher: The Optical Society
Date: 10-03-2015
DOI: 10.1364/OL.40.000994
Publisher: AIP Publishing
Date: 11-2021
DOI: 10.1063/5.0065591
Abstract: We present a mid-IR (λ ∼ 8.3 μm) quantum well infrared photodetector (QWIP) fabricated on a mid-IR transparent substrate, allowing photodetection with illumination from either the front surface or through the substrate. The device is based on a 400 nm-thick GaAs/AlGaAs semiconductor QWIP heterostructure enclosed in a nanostructured metal–insulator–metal cavity and hosted on a mid-IR transparent ZnSe substrate. Metallic stripes are symmetrically patterned by e-beam lithography on both sides of the active region. The detector spectral coverage spans from λ ∼ 7.15 to λ ∼ 8.7 μm by changing the stripe width L—from L = 1.0 to L = 1.3 μm—thus frequency-tuning the optical cavity mode. Both micro-FTIR passive optical characterizations and photocurrent measurements of the two-port system are carried out. They reveal a similar spectral response for the two detector ports with an experimentally measured TBLIP of ∼200 K.
Publisher: Elsevier BV
Date: 03-2002
Publisher: Institution of Engineering and Technology (IET)
Date: 2002
DOI: 10.1049/EL:20021143
Publisher: AIP Publishing
Date: 15-12-2008
DOI: 10.1063/1.3043795
Abstract: We elucidate the effects of the lateral mode structure on the far field pattern of metal-metal ridge-waveguide terahertz quantum cascade lasers. By introducing a 6-μm-wide metal gap on the top metal contact, we suppress odd-parity lateral modes and drastically modify the far field pattern. Measurements are in good qualitative agreement with full three-dimensional finite-difference-time-domain modeling. Experimental evidence of nonuniform current pumping on the intensity distribution of the guided mode (and hence the far field pattern) is also presented and explained in terms of gain guiding.
Publisher: IEEE
Date: 06-2019
Publisher: Wiley
Date: 24-07-2009
DOI: 10.1002/JRS.2352
Publisher: AIP Publishing
Date: 02-02-2009
DOI: 10.1063/1.3076127
Abstract: The two-dimensional concentration and manipulation of micron-scale particles by orthogonal, surface acoustic, standing waves is demonstrated. The particles are organized by liquid pressure waves in a microfluidic system over a piezoelectric substrate and form a uniform two-dimensional array with a spacing governed by the mechanical nodes of the two orthogonal, surface acoustic, standing waves. The nodal spacing can be controlled in each orthogonal direction independently by adjustment of the radio frequency applied to the separate acoustic wave transducers. This technique could be used to enhance the particle concentrations at sensing locations in DNA or protein array detectors.
Publisher: The Optical Society
Date: 04-11-2019
DOI: 10.1364/OE.27.033768
Publisher: Optica Publishing Group
Date: 03-09-2020
Abstract: The accuracy of high-resolution spectroscopy depends critically on the stability, frequency control, and traceability available from laser sources. In this work, we report exact tunable frequency synthesis and phase control of a terahertz laser. The terahertz laser is locked by a terahertz injection phase lock loop for the first time, with the terahertz signal generated by heterodyning selected lines from an all-fiber infrared frequency comb generator in an ultrafast photodetector. The comb line frequency separation is exactly determined by a Global Positioning System-locked microwave frequency synthesizer, providing traceability of the terahertz laser frequency to primary standards. The locking technique reduced the heterodyne linewidth of the terahertz laser to a measurement instrument-limited linewidth of <!-- 1 H z , robust against short- and long-term environmental fluctuations. The terahertz laser frequency can be tuned in increments determined only by the microwave synthesizer resolution, and the phase of the laser, relative to the reference, is independently and precisely controlled within a range ± 0.3 π . These findings are expected to enable applications in phase-resolved high-precision terahertz gas spectroscopy and radiometry.
Publisher: AIP Publishing
Date: 26-03-2012
DOI: 10.1063/1.3697403
Abstract: We demonstrate the directed control of charge carriers in graphene using the electric field that accompanies the propagation of surface acoustic waves (SAWs) on a piezoelectric surface. Graphene grown by chemical vapor deposition was transferred to the surface of lithium niobate, allowing its direct integration with interdigital transducers used for SAW generation and detection. Radio frequency (RF) signal applied to the transducers at their resonant frequency was found to generate a direct current flow by the transport of p-type charge carriers. The acoustically induced current scales linearly with the applied RF power and can be observed even in presence of a counter-flow current induced by an applied bias.
Publisher: Wiley
Date: 23-12-2019
Publisher: Optica Publishing Group
Date: 03-02-2020
DOI: 10.1364/OE.380656
Abstract: The quantum cascade laser is a powerful solid-state source of terahertz-frequency radiation. However, integrating multiple photonic functions into a monolithic platform in this frequency range is non-trivial due to the scaling of photonic structures for the long terahertz wavelengths and the low frequency tuning coefficients of the quantum cascade lasers. Here, we have designed a simple terahertz-frequency photonic integrated circuit by coupling a racetrack resonator with a ridge laser in the longitudinal direction to design a notch filter. The transmission properties of this filter structure are dependent on the phase matching and losses in the coupled racetrack and results in a comb of stopband frequencies. We have optimized the comb separation by carefully selecting the cavity dimensions of the racetrack resonator to suppress longitudinal modes in the ridge laser enabling single-mode emission. The emission frequencies and output power from laser are controlled through appropriate control of drive currents to the ridge and the racetrack resonator. The emission frequency is electrically tuned over ∼81 GHz exploiting Stark shift of the gain as a function of drive current at the ridge laser, coinciding with an output power variation of ∼27% of the peak power (at a heat sink temperature of 50 K). The output power from the ridge also varied by ∼30% and the frequency was tuned by a further 10 GHz when the driving conditions at the ridge laser are invariant and the current at the racetrack resonator was varied. To our best knowledge, this is the first report of a frequency engineering, tuning and power modulation of terahertz-frequency quantum cascade lasers using a photonic integrated circuit.
Publisher: IEEE
Date: 09-2013
Publisher: International Union of Crystallography (IUCr)
Date: 14-12-2010
DOI: 10.1107/S0021889810043372
Abstract: The application of terahertz time-domain spectroscopy and imaging to the study of proteins in crystalline form is demonstrated. Terahertz time-domain spectroscopy is particularly sensitive to the long-range ordering of molecules, with proven utility for the spectroscopy of crystalline biological small molecules. Here, the terahertz time-domain absorption response of a macromolecular protein single crystal is investigated for the first time. In particular, the effect of dehydration on the terahertz absorption coefficient of tetragonal hen egg white lysozyme crystals is reported.
Publisher: IEEE
Date: 09-2013
Publisher: The Optical Society
Date: 09-07-2019
DOI: 10.1364/OE.27.020231
Publisher: The Optical Society
Date: 27-11-2017
Publisher: AIP Publishing LLC
Date: 2015
DOI: 10.1063/1.4915165
Publisher: Springer Science and Business Media LLC
Date: 09-04-2020
DOI: 10.1038/S41377-020-0294-Z
Abstract: Quasi-crystal distributed feedback lasers do not require any form of mirror cavity to lify and extract radiation. Once implemented on the top surface of a semiconductor laser, a quasi-crystal pattern can be used to tune both the radiation feedback and the extraction of highly radiative and high-quality-factor optical modes that do not have a defined symmetric or anti-symmetric nature. Therefore, this methodology offers the possibility to achieve efficient emission, combined with tailored spectra and controlled beam ergence. Here, we apply this concept to a one-dimensional quantum cascade wire laser. By lithographically patterning a series of air slits with different widths, following the Octonacci sequence, on the top metal layer of a double-metal quantum cascade laser operating at THz frequencies, we can vary the emission from single-frequency-mode to multimode over a 530-GHz bandwidth, achieving a maximum peak optical power of 240 mW (190 mW) in multimode (single-frequency-mode) lasers, with record slope efficiencies for multimode surface-emitting disordered THz lasers up to ≈570 mW/A at 78 K and ≈720 mW/A at 20 K and wall-plug efficiencies of η ≈ 1%.
Publisher: AIP Publishing
Date: 07-03-2011
DOI: 10.1063/1.3560980
Abstract: We exploit the modal confinement properties of metal-metal ridge waveguides to investigate the effect of reducing the thickness of the active laser cores in both terahertz and mid-infrared quantum cascade lasers. Devices with active regions over 55 times thinner than the free-space emission wavelength are demonstrated. They show only a modest increase in threshold current density compared with conventional-thickness devices. The limited increase in threshold is possibly due to a parasitic current channel in addition to the radiative current channel. These structures could be useful for the development of ultra-low volume lasers.
Publisher: Optica Publishing Group
Date: 12-2009
Publisher: American Chemical Society (ACS)
Date: 14-05-2020
Publisher: Wiley
Date: 26-01-2010
Abstract: The terahertz frequency spectrum of pentaerythritol tetranitrate (PETN) is calculated using Discover with the COMPASS force field, CASTEP and PWscf. The calculations are compared to each other and to terahertz spectra (0.3-3 THz) of crystalline PETN recorded at 4 K. A number of analysis methods are used to characterise the calculated normal modes.
Publisher: Elsevier BV
Date: 03-2008
Publisher: IEEE
Date: 09-2014
Publisher: SPIE
Date: 23-02-2013
DOI: 10.1117/12.2000743
Publisher: AIP Publishing
Date: 02-11-2009
DOI: 10.1063/1.3253714
Publisher: Springer Science and Business Media LLC
Date: 20-04-2023
Publisher: IEEE
Date: 12-2015
Publisher: The Optical Society
Date: 27-01-2016
DOI: 10.1364/OE.24.002174
Publisher: Springer Science and Business Media LLC
Date: 08-08-2010
DOI: 10.1038/NMAT2822
Abstract: Surface plasmons have found a broad range of applications in photonic devices at visible and near-infrared wavelengths. In contrast, longer-wavelength surface electromagnetic waves, known as Sommerfeld or Zenneck waves, are characterized by poor confinement to surfaces and are therefore difficult to control using conventional metallo-dielectric plasmonic structures. However, patterning the surface with subwavelength periodic features can markedly reduce the asymptotic surface plasmon frequency, leading to 'spoof' surface plasmons with subwavelength confinement at infrared wavelengths and beyond, which mimic surface plasmons at much shorter wavelengths. We demonstrate that by directly sculpting designer spoof surface plasmon structures that tailor the dispersion of terahertz surface plasmon polaritons on the highly doped semiconductor facets of terahertz quantum cascade lasers, the performance of the lasers can be markedly enhanced. Using a simple one-dimensional grating design, the beam ergence of the lasers was reduced from approximately 180 degrees to approximately 10 degrees, the directivity was improved by over 10 decibels and the power collection efficiency was increased by a factor of about six compared with the original unpatterned devices. We achieve these improvements without compromising high-temperature performance of the lasers.
Publisher: SPIE
Date: 27-01-2017
DOI: 10.1117/12.2251405
Publisher: Optica Publishing Group
Date: 2004
DOI: 10.1364/OL.29.000122
Abstract: Quantum-cascade lasers operating at 4.7, 3.5, and 2.3 THz have been used to achieve cyclotron resonance in InAs and InSb quantum wells from liquid-helium temperatures to room temperature. This represents one of the first spectroscopic applications of terahertz quantum-cascade lasers. Results show that these compact lasers are convenient and reliable sources with adequate power and stability for this type of far-infrared magneto-optical study of solids. Their compactness promises interesting future applications in solid-state spectroscopy.
Publisher: IEEE
Date: 5
Publisher: Optica Publishing Group
Date: 26-05-2020
DOI: 10.1364/OE.391656
Abstract: We report on the design, fabrication and characterisation of large-area photoconductive THz array structures, consisting of a thin LT-GaAs active region transferred to an insulating substrate using a wafer-scale bonding process. The electrically insulating, transparent substrate reduces the parasitic currents in the devices, allowing peak THz-fields as high as 120 kV cm −1 to be generated over a bandwidth THz. These results are achieved using lower pulse energies than demanded by conventional photoconductive arrays and other popular methods of generating high-field THz radiation. Two device sizes are fully characterised and the emission properties are compared to generation by optical rectification in ZnTe. The device can be operated in an optically saturated regime in order to suppress laser noise.
Publisher: AIP Publishing
Date: 10-05-2010
DOI: 10.1063/1.3427191
Abstract: We demonstrate the generation of broadband terahertz (THz) frequency radiation from photoconductive emitters formed from Fe-doped InGaAs (Fe:InGaAs), grown by metal-organic chemical vapor deposition, following pulsed (femtosecond) laser excitation at wavelengths ranging from 830 nm to 1.55 μm. The Fe is incorporated epitaxially during growth, giving precise control over the doping level. Using both single-crystal ZnTe and GaP electro-optic detectors over the same wavelength range, the emission spectra from several Fe:InGaAs wafers with different Fe content were measured, with THz emission from all wafers showing bandwidths in excess of 2.0 THz. The THz output power was found to be strongly dependant on the Fe content, the thickness of the Fe:InGaAs layer, and the excitation wavelength.
Publisher: IEEE
Date: 05-2008
Publisher: Elsevier BV
Date: 1992
Publisher: IEEE
Date: 10-2011
Publisher: International Union of Crystallography (IUCr)
Date: 25-12-2013
DOI: 10.1107/S1600576713029506
Abstract: The effect of temperature on the terahertz-frequency-range material properties of lyophilized and single-crystal hen egg-white lysozyme has been measured using terahertz time-domain spectroscopy, with the results presented and discussed in the context of protein and solvent dynamical and glass transitions. Lyophilized hen egg-white lysozyme was measured over a temperature range from 4 to 290 K, and a change in the dynamical behaviour of the s le at around 100 K was observed through a change in the terahertz absorption spectrum. Additionally, the effect of cryoprotectants on the temperature-dependent absorption coefficient is studied, and it is demonstrated that terahertz time-domain spectroscopy is capable of resolving the true glass transition temperature of single-crystal hen egg-white lysozyme at ∼150 K, which is in agreement with literature values measured using differential scanning calorimetry.
Publisher: IEEE
Date: 10-2011
Publisher: IEEE
Date: 2002
Publisher: The Optical Society
Date: 04-11-2015
Publisher: AIP
Date: 2011
DOI: 10.1063/1.3666708
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2008
Publisher: Optica Publishing Group
Date: 26-10-2009
DOI: 10.1364/OE.17.020631
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2018
Publisher: AIP Publishing
Date: 08-07-2014
DOI: 10.1063/1.1768313
Abstract: We report the coherent generation and detection of ultrabroadband terahertz (THz) radiation using low-temperature-grown GaAs photoconductive antennas as both emitters and receivers. THz radiation with frequency components over 15THz was obtained, the highest reported for a THz time-domain system based on photoconductive antennas. Such a system has a smooth spectral distribution between 0.3 and 7.5THz, ideal for spectroscopic applications. In addition, sharp spectral features at 8.0 and 8.8THz were observed, and explained in terms of optical phonon resonances in the photoconductive antennas.
Publisher: Elsevier BV
Date: 06-2004
Publisher: IOP Publishing
Date: 17-06-2003
DOI: 10.1088/0031-9155/48/13/313
Abstract: Fourier-transform infrared transmission spectroscopy has been used for the determination of glucose concentration in whole blood s les from 28 patients. A 4-vector partial least-squares calibration model, using the spectral range 950-1200 cm(-1), yielded a standard-error-of-prediction of 0.59 mM for an independent test set. For blood s les from a single patient, we found that the glucose concentration was proportional to the difference between the values of the second derivative spectrum at 1082 cm(-1) and 1093 cm(-1). This indicates that spectroscopy at these two specific wavenumbers alone could be used to determine the glucose concentration in blood plasma s les from a single patient, with a prediction error of 0.95 mM.
Publisher: AIP Publishing
Date: 30-08-2004
DOI: 10.1063/1.1789244
Publisher: IOP Publishing
Date: 24-03-2009
DOI: 10.1088/0957-4484/20/15/155304
Abstract: We demonstrate a new process for fabricating embedded co-planar electrodes which combines top-down with bottom-up approaches to nanofabrication. The co-planarity of the electrodes with the substrate surface is achieved by deposition of a dielectric filling layer around a set of lithographically defined metallic electrodes. In order to prevent adhesion of the dielectric to the pre-defined electrodes, an adhesion inhibiting layer, based on a self-assembled monolayer, is formed specifically on the electrode surface prior to deposition of the dielectric. For monolayers with an acid functional group, this adhesion inhibitor yields almost complete non-adhesion of the dielectric filling layer.
Publisher: IEEE
Date: 09-2018
Publisher: The Optical Society
Date: 25-04-2017
DOI: 10.1364/OE.25.010177
Publisher: AIP Publishing
Date: 30-04-2018
DOI: 10.1063/1.5027202
Abstract: Tapered coplanar waveguides with integrated photoconductors were designed, fabricated, and measured, with pulsed transmission results comparing well with High Frequency Structure Simulator simulations which predict increased confinement and electric field concentration in the tapered region. Devices made with titanium/gold metallisation were used to demonstrate transmission and confinement, while the magnetoresistive properties of devices with cobalt/copper multilayers were used to demonstrate the field concentration. In the latter case, a mathematical framework was developed to understand the relationship between tapering effects and the picosecond magnetoresistance response.
Publisher: Wiley
Date: 13-05-2021
Abstract: Quantum cascade lasers (QCLs) represent a fascinating accomplishment of quantum engineering and enable the direct generation of terahertz (THz) frequency radiation from an electrically biased semiconductor heterostructure. Their large spectral bandwidth, high output powers, and quantum‐limited linewidths have facilitated the realization of THz pulses by active mode‐locking and passive generation of optical frequency combs (FCs) through intracavity four‐wave‐mixing, albeit over a restricted operational regime. Here, an integrated architecture is conceived for the generation of high power (5.5–8.0 mW) THz FCs comprising an ultrafast THz polaritonic reflector, exploiting intersubband (ISB) cavity polaritons, and a broad bandwidth (2.3–3.8 THz) heterogenous THz QCL. By tuning the group‐delay‐dispersion in an integrated geometry, through the exploitation of light‐induced bleaching of the ISB‐based THz polaritons, spectral reshaping of the QCL emission and stable FC operation over an operational range up to 38%, characterized by a single and narrow (down to 700 Hz) intermode beatnote are demonstrated. This concept provides design guidelines for a new generation of compact, cost‐effective, electrically driven chip‐scale FC sources based on ultrafast polariton dynamics, paving the way toward the generation of mode‐locked THz microlasers that can strongly impact a broad range of applications in ultrafast sciences, data storage, high‐speed communication, and spectroscopy.
Publisher: AIP Publishing
Date: 11-2004
DOI: 10.1063/1.1810217
Abstract: We report high power quantum cascade lasers operating above liquid nitrogen temperature at λ≃87 and 130μm based on a bound-to-continuum transition. For λ≃87μm, 56mW peak power in pulsed operation and 50mW continuous wave operation at 10K are demonstrated. At λ≃130μm, a peak power of 50mW was achieved and devices operated in continuous wave reached a maximum temperature of 53K with an optical power of 11.5mW at T=10K. Lifetimes are extracted from the scaling of the transport and laser parameters as a function of size using a simple rate equation model.
Publisher: American Physical Society (APS)
Date: 15-12-1991
Publisher: IEEE
Date: 09-2019
Publisher: IEEE
Date: 12-2010
Publisher: IEEE
Date: 08-2017
Publisher: OSA
Date: 2015
Publisher: OSA
Date: 2015
Publisher: Elsevier BV
Date: 07-1994
Publisher: IEEE
Date: 08-2015
Publisher: Springer Science and Business Media LLC
Date: 26-03-2018
DOI: 10.1038/NATURE25790
Abstract: Room-temperature operation is essential for any optoelectronics technology that aims to provide low-cost, compact systems for widespread applications. A recent technological advance in this direction is bolometric detection for thermal imaging, which has achieved relatively high sensitivity and video rates (about 60 hertz) at room temperature. However, owing to thermally induced dark current, room-temperature operation is still a great challenge for semiconductor photodetectors targeting the wavelength band between 8 and 12 micrometres, and all relevant applications, such as imaging, environmental remote sensing and laser-based free-space communication, have been realized at low temperatures. For these devices, high sensitivity and high speed have never been compatible with high-temperature operation. Here we show that a long-wavelength (nine micrometres) infrared quantum-well photodetector fabricated from a metamaterial made of sub-wavelength metallic resonators exhibits strongly enhanced performance with respect to the state of the art up to room temperature. This occurs because the photonic collection area of each resonator is much larger than its electrical area, thus substantially reducing the dark current of the device. Furthermore, we show that our photonic architecture overcomes intrinsic limitations of the material, such as the drop of the electronic drift velocity with temperature, which constrains conventional geometries at cryogenic operation. Finally, the reduced physical area of the device and its increased responsivity allow us to take advantage of the intrinsic high-frequency response of the quantum detector at room temperature. By mixing the frequencies of two quantum-cascade lasers on the detector, which acts as a heterodyne receiver, we have measured a high-frequency signal, above four gigahertz (GHz). Therefore, these wide-band uncooled detectors could benefit technologies such as high-speed (gigabits per second) multichannel coherent data transfer and high-precision molecular spectroscopy.
Publisher: American Chemical Society (ACS)
Date: 26-03-2021
Publisher: AIP Publishing
Date: 22-02-2016
DOI: 10.1063/1.4942452
Abstract: The gain recovery time of a bound-to-continuum terahertz frequency quantum cascade laser, operating at 1.98 THz, has been measured using broadband terahertz-pump-terahertz-probe spectroscopy. The recovery time is found to reduce as a function of current density, attaining a value of 18 ps as the laser is brought close to threshold. We attribute this reduction to improved coupling efficiency between the injector state and the upper lasing level as the active region aligns.
Publisher: IEEE
Date: 09-2009
Publisher: IEEE
Date: 09-2006
Publisher: Springer Science and Business Media LLC
Date: 04-2006
Publisher: IEEE
Date: 12-2012
Publisher: AIP Publishing
Date: 04-03-2003
DOI: 10.1063/1.1559419
Abstract: The cw operation of chirped-superlattice quantum-cascade lasers emitting at λ∼67 μm (4.4 THz) is analyzed. Collected (min. 33% efficiency) output powers of 4 mW per facet are measured at liquid helium temperatures and a maximum operating temperature of 48 K is reached. Under pulsed excitation at duty cycles of 0.5%–1%, slightly higher (10%) peak powers are reached, and the device can be operated up to 67 K. Low threshold current densities of 165 and 185 A cm−2 are observed in pulsed and cw operation, respectively. The operation of the laser is examined using the Hakki–Paoli technique to estimate the net gain of the structure.
Publisher: The Optical Society
Date: 17-10-2014
DOI: 10.1364/BOE.5.003981
Publisher: IEEE
Date: 2000
Publisher: Elsevier BV
Date: 2002
Publisher: American Chemical Society (ACS)
Date: 20-07-2017
DOI: 10.1021/ACS.ANALCHEM.7B01235
Abstract: Terahertz-frequency-range measurements can offer potential insight into the picosecond dynamics, and therefore function, of many chemical systems. There is a need to develop technologies capable of performing such measurements in aqueous and polar environments, particularly when it is necessary to maintain the full functionality of biological s les. In this study, we present a proof-of-concept technology comprising an on-chip planar Goubau line, integrated with a microfluidic channel, which is capable of low-loss, terahertz-frequency-range spectroscopic measurements of liquids. We also introduce a mathematical model that accounts for changes in the electric field distribution around the waveguide, allowing accurate, frequency-dependent liquid parameters to be extracted. We demonstrate the sensitivity of this technique by measuring a homologous alcohol series across the 0.1-0.8 THz frequency range.
Publisher: MDPI AG
Date: 20-05-2016
Publisher: IEEE
Date: 09-2010
Publisher: IEEE
Date: 09-2009
Publisher: Institution of Engineering and Technology (IET)
Date: 2010
DOI: 10.1049/EL.2010.3575
Publisher: IEEE
Date: 09-2010
Publisher: OSA
Date: 2014
Publisher: AIP Publishing
Date: 08-2013
DOI: 10.1063/1.4816736
Abstract: We present the self-aligned fabrication of on-chip devices in which waveguides, incorporating integrated photoconductive switches, are combined with two-dimensional electron systems to allow probing of the ultrafast (terahertz frequency range) properties of confined semiconductor systems, both at cryogenic temperatures and in high magnetic fields. We demonstrate the direct injection of on-chip terahertz pulses into the mesoscopic system by femtosecond, near infra-red laser excitation of in-plane photoconductive switches formed on an epitaxially grown, low-temperature GaAs layer, which is integrated monolithically with a GaAs/AlGaAs heterostructure containing a two-dimensional electron system. Both the input and output terahertz signals of an on-chip waveguide are s led by altering dynamically the photoconductive excitation/detection arrangement in situ on a single device. We also demonstrate a new method for sub-Kelvin excitation and detection of on-chip terahertz frequency radiation in a 3He/4He dilution refrigerator that allows the photocurrent and detected terahertz transient to be mapped as function of the near-infrared excitation position at the emitter and the detector, respectively. Furthermore, we demonstrate transmission of terahertz transients through a two-dimensional electron system in a coplanar waveguide under magnetic field at temperatures as low as 200 mK.
Publisher: Elsevier BV
Date: 02-1994
Publisher: Cambridge University Press (CUP)
Date: 08-05-2019
DOI: 10.1017/S175907871900028X
Abstract: Antenna-pattern measurements obtained from a double-metal supra-terahertz-frequency (supra-THz) quantum cascade laser (QCL) are presented. The QCL is mounted within a mechanically micro-machined waveguide cavity containing dual diagonal feedhorns. Operating in continuous-wave mode at 3.5 THz, and at an ambient temperature of ~60 K, QCL emission has been directed via the feedhorns to a supra-THz detector mounted on a multi-axis linear scanner. Comparison of simulated and measured far-field antenna patterns shows an excellent degree of correlation between beamwidth (full-width-half-maximum) and sidelobe content and a very substantial improvement when compared with unmounted devices. Additionally, a single output has been used to successfully illuminate and demonstrate an optical breadboard arrangement associated with a future supra-THz Earth observation space-borne payload. Our novel device has therefore provided a valuable demonstration of the effectiveness of supra-THz diagonal feedhorns and QCL devices for future space-borne ultra-high-frequency Earth-observing heterodyne radiometers.
Publisher: SAGE Publications
Date: 06-2007
DOI: 10.1366/000370207781269701
Abstract: Broadband terahertz time-domain spectroscopy (THz-TDS) has been used to measure the far-infrared (FIR) vibrational spectra of several commonly used pure explosives, including 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), 1,3-dinitrato-2,2-bis(nitratomethyl)-propane (PETN), and two types of plastic explosive, SEMTEX and SX2. A number of distinct absorption peaks, originating from FIR-active vibrational modes of these polycrystalline energetic materials, were observed in the frequency range 0.3–7.5 THz (10–250 cm −1 ). In addition, the temperature-dependent FIR vibrational spectra of PETN were measured between 4 K and 296 K with several well-resolved absorption peaks observed across this temperature range. We find that as the temperature is reduced, the observed absorption peaks resolve into narrower features and shift towards higher frequencies. The temperature dependence of the spectra is explained in terms of the anharmonicity of the vibrational potentials of crystalline compounds, and an empirical fit is given to describe the peak shift with temperature.
Publisher: The Optical Society
Date: 25-04-2017
DOI: 10.1364/OE.25.010153
Publisher: SPIE
Date: 05-10-2007
DOI: 10.1117/12.739281
Publisher: AIP Publishing
Date: 22-08-2011
DOI: 10.1063/1.3629991
Abstract: There has been growing interest in the use of terahertz (THz) quantum cascade lasers (QCLs) for sensing applications. However, the lack of compact and sensitive THz detectors has limited the potential for commercial exploitation of sensors based on these devices. We have developed a self-mixing sensing technique in which THz QCLs are used for both generation and interferometric sensing of THz radiation, eliminating the need for a separate detector. Using this technique, we have measured the displacement of a remote target, both with and without opaque (in the visible spectrum) materials in the beam path and demonstrated a stand-off distance of up to 7 m in air.
Publisher: Elsevier BV
Date: 04-2008
Publisher: IEEE
Date: 09-2012
Publisher: IEEE
Date: 09-2010
Publisher: IEEE
Date: 09-2010
Publisher: The Optical Society
Date: 10-02-2015
DOI: 10.1364/OE.23.004012
Publisher: IEEE
Date: 09-2012
Publisher: Springer Science and Business Media LLC
Date: 16-03-2018
DOI: 10.1038/S41467-018-03440-4
Abstract: Terahertz (THz) quantum cascade lasers (QCLs) have undergone rapid development since their demonstration, showing high power, broad-tunability, quantum-limited linewidth, and ultra-broadband gain. Typically, to address applications needs, continuous-wave (CW) operation, low- ergent beam profiles and fine spectral control of the emitted radiation, are required. This, however, is very difficult to achieve in practice. Lithographic patterning has been extensively used to this purpose (via distributed feedback (DFB), photonic crystals or microcavities), to optimize either the beam ergence or the emission frequency, or, both of them simultaneously, in third-order DFBs, via a demanding fabrication procedure that precisely constrains the mode index to 3. Here, we demonstrate wire DFB THz QCLs, in which feedback is provided by a sinusoidal corrugation of the cavity, defining the frequency, while light extraction is ensured by an array of surface holes. This new architecture, extendable to a broad range of far-infrared frequencies, has led to the achievement of low- ergent beams (10°), single-mode emission, high slope efficiencies (250 mW/A), and stable CW operation.
Publisher: The Optical Society
Date: 28-08-2012
DOI: 10.1364/OE.20.020855
Publisher: The Optical Society
Date: 06-01-2017
DOI: 10.1364/OE.25.000486
Publisher: Elsevier BV
Date: 06-2004
Publisher: AIP Publishing
Date: 12-11-2003
DOI: 10.1063/1.1627485
Abstract: We report the operation of a pulsed terahertz (THz) imaging system that uses a 120 fs pulse-width laser operating at 1.06 μm, and photoconductive InGaAs emitters and detectors. THz images are presented of biological and nonbiological specimens. The signal-to-noise ratio and frequency range of this system are compared to those obtained from existing pulsed imaging systems based on 0.8 μm excitation.
Publisher: Springer Science and Business Media LLC
Date: 15-03-2016
DOI: 10.1038/SREP23053
Abstract: Mode-locked comb sources operating at optical frequencies underpin applications ranging from spectroscopy and ultrafast physics, through to absolute frequency measurements and atomic clocks. Extending their operation into the terahertz frequency range would greatly benefit from the availability of compact semiconductor-based sources. However, the development of any compact mode-locked THz laser, which itself is inherently a frequency comb, has yet to be achieved without the use of an external stimulus. High-power, electrically pumped quantum cascade lasers (QCLs) have recently emerged as a promising solution, owing to their octave spanning bandwidths, the ability to achieve group-velocity dispersion compensation and the possibility of obtaining active mode-locking. Here, we propose an unprecedented compact architecture to induce both frequency and litude self-modulation in a THz QCL. By engineering a microwave avalanche oscillator into the laser cavity, which provides a 10 GHz self-modulation of the bias current and output power, we demonstrate multimode laser emission centered around 3 THz, with distinct multiple sidebands. The resulting microwave litude and frequency self-modulation of THz QCLs opens up intriguing perspectives, for engineering integrated self-mode-locked THz lasers, with impact in fields such as nano- and ultrafast photonics and optical metrology.
Publisher: American Chemical Society (ACS)
Date: 02-04-2019
Publisher: The Optical Society
Date: 05-02-2018
DOI: 10.1364/OE.26.003814
Publisher: SPIE-Intl Soc Optical Eng
Date: 02-10-2014
Publisher: The Optical Society
Date: 07-2011
DOI: 10.1364/OL.36.002587
Publisher: Springer Science and Business Media LLC
Date: 03-07-2023
DOI: 10.1038/S41467-023-39594-Z
Abstract: In the majority of optoelectronic devices, emission and absorption of light are considered as perturbative phenomena. Recently, a regime of highly non-perturbative interaction, ultra-strong light-matter coupling, has attracted considerable attention, as it has led to changes in the fundamental properties of materials such as electrical conductivity, rate of chemical reactions, topological order, and non-linear susceptibility. Here, we explore a quantum infrared detector operating in the ultra-strong light-matter coupling regime driven by collective electronic excitations, where the renormalized polariton states are strongly detuned from the bare electronic transitions. Our experiments are corroborated by microscopic quantum theory that solves the problem of calculating the fermionic transport in the presence of strong collective electronic effects. These findings open a new way of conceiving optoelectronic devices based on the coherent interaction between electrons and photons allowing, for ex le, the optimization of quantum cascade detectors operating in the regime of strongly non-perturbative coupling with light.
Publisher: Springer Science and Business Media LLC
Date: 04-05-2016
DOI: 10.1038/SREP24811
Abstract: Diffraction is the ultimate limit at which details of objects can be resolved in conventional optical spectroscopy and imaging systems. In the THz spectral range, spectroscopy systems increasingly rely on ultra-broadband radiation (extending over more 5 octaves) making a great challenge to reach resolution limited by diffraction. Here, we propose an original easy-to-implement wavefront manipulation concept to achieve ultrabroadband THz spectroscopy system with diffraction-limited resolution. Applying this concept to a large-area photoconductive emitter, we demonstrate diffraction-limited ultra-broadband spectroscopy system up to 14.5 THz with a dynamic range of 10 3 . The strong focusing of ultrabroadband THz radiation provided by our approach is essential for investigating single micrometer-scale objects such as graphene flakes or living cells and besides for achieving intense ultra-broadband THz electric fields.
Publisher: IEEE
Date: 09-2008
Publisher: American Chemical Society (ACS)
Date: 12-12-2016
Publisher: AIP Publishing
Date: 13-07-2020
DOI: 10.1063/5.0013505
Abstract: We report the realization of controllable linear-to-circular polarization states in single-mode terahertz master-oscillator power- lifier quantum cascade lasers (THz-MOPA-QCLs). The MOPA device contains a first-order distributed feedback (DFB) laser as the master-oscillator, a pre lifier, and a 2D periodical antenna array as the power extractor. The polarization state is determined by the orientation and the phase relationship between the antennas. The antenna array is carefully designed to efficiently extract the THz radiation and not to induce field oscillation in the array or influence the mode oscillation in the DFB section. Each demonstrated device exhibits single-mode emission with a side mode suppression ratio of ∼26 dB and a single-lobed beam with a low ergence of ∼23°×30°. Realized in different devices, the degree of linear or circular polarization reaches as high as 97.5% or 99.3%. Both the operation frequency and the polarization state of the radiation are lithographically tunable.
Publisher: Springer Science and Business Media LLC
Date: 11-02-2020
DOI: 10.1038/S41467-020-14662-W
Abstract: The fast modulation of lasers is a fundamental requirement for applications in optical communications, high-resolution spectroscopy and metrology. In the terahertz-frequency range, the quantum-cascade laser (QCL) is a high-power source with the potential for high-frequency modulation. However, conventional electronic modulation is limited fundamentally by parasitic device impedance, and so alternative physical processes must be exploited to modulate the QCL gain on ultrafast timescales. Here, we demonstrate an alternative mechanism to modulate the emission from a QCL device, whereby optically-generated acoustic phonon pulses are used to perturb the QCL bandstructure, enabling fast litude modulation that can be controlled using the QCL drive current or strain pulse litude, to a maximum modulation depth of 6% in our experiment. We show that this modulation can be explained using perturbation theory analysis. While the modulation rise-time was limited to ~800 ps by our measurement system, theoretical considerations suggest considerably faster modulation could be possible.
Publisher: Springer Science and Business Media LLC
Date: 30-11-2018
DOI: 10.1038/S41467-018-07629-5
Abstract: The original version of this Article contained an error in the Acknowledgements, which incorrectly omitted the following: ‘We also acknowledge support from the Australian Research Council’s Discovery Projects Funding Scheme (Grant DP 160 103910).’ This has been corrected in both the PDF and HTML versions of the Article.
Publisher: American Chemical Society (ACS)
Date: 07-03-2014
DOI: 10.1021/NN405281S
Publisher: The Optical Society
Date: 18-01-2018
DOI: 10.1364/OE.26.001942
Publisher: The Optical Society
Date: 16-12-2013
DOI: 10.1364/OE.21.031872
Publisher: AIP Publishing
Date: 02-12-2019
DOI: 10.1063/1.5116351
Abstract: We demonstrate a sensitive and compact terahertz heterodyne detection system based on a quantum cascade laser (QCL) as a local oscillator and a hot electron bolometer (HEB) as a mixer. It relies on an original optical coupling scheme where the terahertz (THz) signal to be detected and the local oscillator (LO) signal are coupled to the HEB from both sides of the integrated lens/antenna mixer. The THz signal of interest impinges on the front side through the silicon lens while the LO onto the rear (air) side. This concept allows us to remove the beam splitter usually employed in terahertz heterodyne receivers. The mixer consists of a Niobium Nitride HEB with a log-spiral planar antenna mounted on the flat side of a hyperhemispherical silicon lens. The local oscillator of the heterodyne detector is a low power consumption and low beam ergence 3rd-order distributed feedback laser with single mode emission at the target frequency of 2.7 THz. The coupling between the QCL and the HEB has been further optimized, using a dielectric hollow waveguide that reliably increases the laser beam directivity and permits us to pump the HEB into its most sensitive state through the air side of the planar antenna. We have measured a noncorrected double sideband receiver noise temperature of 880 K at 2.7 THz.
Publisher: AIP Publishing
Date: 03-04-2017
DOI: 10.1063/1.4979536
Abstract: Interdigitated photoconductive (iPC) switches are powerful and convenient devices for time-resolved spectroscopy, with the ability to operate both as sources and detectors of terahertz (THz) frequency pulses. However, reflection of the emitted or detected radiation within the device substrate itself can lead to echoes that inherently limit the spectroscopic resolution achievable for their use in time-domain spectroscopy (TDS) systems. In this work, we demonstrate a design of low-temperature-grown-GaAs (LT-GaAs) iPC switches for THz pulse detection that suppresses such unwanted echoes. This is realized through the growth of a buried multilayer LT-GaAs structure that retains its ultrafast properties, which, after wafer bonding to a metal-coated host substrate, results in an iPC switch with a metal plane buried at a subwavelength depth below the LT-GaAs surface. Using this device as a detector, and coupling it to an echo-less iPC source, enables echo-free THz-TDS and high-resolution spectroscopy, with a resolution limited only by the temporal length of the measurement governed by the mechanical delay line used. As a proof-of-principle, the 212-221 and the 101-212 rotational lines of water vapor have been spectrally resolved, demonstrating a spectral resolution below 10 GHz.
Publisher: IEEE
Date: 05-2007
Publisher: Institution of Engineering and Technology (IET)
Date: 2003
Abstract: Dielectrophoretic manipulation enables the positioning and orientation of DNA molecules for nanometer-scale applications. However, the dependence of the dielectrophoretic force and torque on the electric field magnitude and frequency has to be well characterised to realise fully the potential of this technique. DNA in solution is attracted to the strongest electric field gradient (i.e. the electrode edge) as a result of the dielectrophoretic force, while the dielectrophoretic torque aligns the DNA with its longest axis parallel to the electric field. In this work, the authors attached -DNA fragments (48 and 25 kilobases) to an array of gold microelectrodes via a terminal thiol bond and characterised the orientation and elongation as a function of electric field magnitude (0.1-0.8 MVm) and frequency (0.08-1.1 MHz). Maximum elongation was observed between 200 and 500 kHz for the attached DNA. Dielectrophoresis is limited by thermal randomisation at electric fields below 0.1 MVm and by electrothermal effects above 0.7 MVm. The authors conclude that dielectrophoresis can be used to manipulate surface-immobilised DNA reproducibly.
Publisher: American Chemical Society (ACS)
Date: 18-09-2012
DOI: 10.1021/LA3025149
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 04-2003
Publisher: IOP Publishing
Date: 21-08-2012
DOI: 10.1088/0957-4484/23/36/365301
Abstract: Molecular self-assembly inherent to many biological molecules, in conjunction with suitable molecular scaffolds to facilitate programmable positioning of nanoscale objects, offers a promising approach for the integration of functional nanoscale complexes into macroscopic host devices. Here, we report the use of the protein RecA as a means of highly efficient programmable patterning of double-stranded (ds)DNA molecules with molecular-scale precision at specific locations along the DNA strand. RecA proteins form nucleoprotein filaments with single-stranded (ss)DNA molecules, which are chosen to be of sequence homologous to the desired binding region on the dsDNA scaffold. We show that the patterning yield can be in excess of 85% and we demonstrate that concurrent patterning of multiple locations on the same dsDNA scaffold can be achieved with separation between the assembled nucleoprotein filaments of less than 4 nm. This is an important prerequisite for this programmable and flexible DNA scaffold patterning technique to be employed in molecular- and nanoscale assembly applications.
Publisher: Springer Science and Business Media LLC
Date: 03-08-2017
DOI: 10.1038/S41598-017-07432-0
Abstract: The effects of optical feedback (OF) in lasers have been observed since the early days of laser development. While OF can result in undesirable and unpredictable operation in laser systems, it can also cause measurable perturbations to the operating parameters, which can be harnessed for metrological purposes. In this work we exploit this ‘self-mixing’ effect to infer the emission spectrum of a semiconductor laser using a laser-feedback interferometer, in which the terminal voltage of the laser is used to coherently s le the reinjected field. We demonstrate this approach using a terahertz frequency quantum cascade laser operating in both single- and multiple-longitudinal mode regimes, and are able to resolve spectral features not reliably resolved using traditional Fourier transform spectroscopy. We also investigate quantitatively the frequency perturbation of in idual laser modes under OF, and find excellent agreement with predictions of the excess phase equation central to the theory of lasers under OF.
Publisher: AIP Publishing
Date: 19-04-2016
DOI: 10.1063/1.4946845
Abstract: We demonstrate the generation of continuous wave terahertz (THz) frequency radiation from photomixers fabricated on both Fe-doped InGaAs and Fe-doped InGaAsP, grown by metal-organic chemical vapor deposition. The photomixers were excited using a pair of distributed Bragg reflector lasers with emission around 1550 nm, and THz radiation was emitted over a bandwidth of greater than 2.4 THz. Two InGaAs and four InGaAsP wafers with different Fe doping concentrations were investigated, with the InGaAs material found to outperform the InGaAsP in terms of emitted THz power. The dependencies of the emitted power on the photomixer applied bias, incident laser power, and material doping level were also studied.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 04-2018
Publisher: IEEE
Date: 09-2010
Publisher: IEEE
Date: 08-2017
Publisher: IEEE
Date: 06-2017
Publisher: AIP Publishing
Date: 09-2021
DOI: 10.1063/5.0056487
Abstract: The phenomenon of self-pulsation (SP) in terahertz (THz) quantum cascade lasers (QCLs) due to optical feedback was reported recently. In this Letter, we propose a THz imaging modality using the SP phenomenon in a THz QCL. We explore the theoretical oscillation properties of the SP scheme and demonstrate its suitability to perform imaging experimentally. The SP imaging scheme operates in self-detection mode, eliminating the need for an external detector. Moreover, the scheme requires only a fixed current, meaning that one can avoid many of the pitfalls associated with high temperature operation of THz QCLs, including frequency chirp and mode hops caused by sweeping the laser current. This also means that one is free to locate the operating point at the maximum power, to produce the desired beam profile or for highest spectral purity, depending on the application. The SP imaging modality proposed in this work can be translated directly to high operating temperature THz QCLs.
Publisher: Optica Publishing Group
Date: 2006
DOI: 10.1364/OE.14.011672
Abstract: We investigate the implementation of surface emission via a second order grating in terahertz quantum cascade lasers with double-metal waveguides. Absorbing edge structures are designed to enforce anti-reflecting boundary conditions, which ensure distributed feedback in the cavity. The grating duty cycle is chosen in order to maximize slope efficiency. Fabricated devices demonstrate surface emission output powers that are comparable to those measured from edge-emitting double metal waveguide structures without gratings. The slope efficiency of surface emitting lasers is twice that of double-metal edge emitting structures. Surface emitting lasers show single mode behavior, with a beam ergence of approximately six degrees.
Publisher: American Physical Society (APS)
Date: 12-2004
Publisher: AIP Publishing
Date: 21-01-2004
DOI: 10.1063/1.1641165
Abstract: We demonstrated a GaAs/AlGaAs-based far-infrared quantum well infrared photodetector at a wavelength of λ=84 μm. The relevant intersubband transition is slightly diagonal with a dipole matrix element of 3.0 nm. At 10 K, a responsivity of 8.6 mA/W and a detectivity of 5×107 cm √Hz/W have been achieved and successful detection up to a device temperature of 50 K has been observed. Being designed for zero bias operation, this device profits from a relatively low dark current and a good noise behavior.
Publisher: The Optical Society
Date: 22-04-2014
DOI: 10.1364/OL.39.002629
Publisher: IEEE
Date: 2000
Publisher: American Physical Society (APS)
Date: 18-03-2002
Publisher: Elsevier BV
Date: 04-2022
Publisher: The Optical Society
Date: 27-06-2014
DOI: 10.1364/OL.39.003962
Publisher: Springer Science and Business Media LLC
Date: 03-07-2019
DOI: 10.1038/S41467-019-10913-7
Abstract: Miniaturized frequency comb sources across hard-to-access spectral regions, i.e. mid- and far-infrared, have long been sought. Four-wave-mixing based Quantum Cascade Laser combs (QCL-combs) are ideal candidates, in this respect, due to the unique possibility to tailor their spectral emission by proper nanoscale design of the quantum wells. We demonstrate full-phase-stabilization of a QCL-comb against the primary frequency standard, proving independent and simultaneous control of the two comb degrees of freedom (modes spacing and frequency offset) at a metrological level. Each emitted mode exhibits a sub-Hz relative frequency stability, while a correlation analysis on the modal phases confirms the high degree of coherence in the device emission, over different power-cycles and over different days. The achievement of fully controlled, phase-stabilized QCL-comb emitters proves that this technology is mature for metrological-grade uses, as well as for an increasing number of scientific and technological applications.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2017
Publisher: AIP Publishing
Date: 06-05-2003
DOI: 10.1063/1.1571653
Abstract: We report terahertz frequency (3.5 THz, λ≃87 μm) emission from quantum-cascade lasers employing a bound-to-continuum transition in the active region. The maximum operating temperature is in excess of 90 K. Peak powers of 20 mW at 20 K and 10 mW at 77 K are achieved. The same devices show continuous-wave operation up to 55 K with measured optical powers of 15 mW at 10 K.
Publisher: OSA
Date: 2018
Publisher: AIP Publishing
Date: 20-03-2004
DOI: 10.1063/1.1628389
Abstract: We demonstrate the critical effect of postgrowth annealing temperature on the properties of low-temperature-grown GaAs. By using annealing temperatures substantially below the 500–600 °C commonly reported, GaAs with high resistivity and with carrier lifetimes as short as 100 fs can be routinely obtained. We discuss the optimum, but different, anneal conditions required for terahertz photoconductive emitters and detectors, and illustrate their use in a continuous-wave system.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2009
Publisher: IEEE
Date: 09-2008
Publisher: American Physical Society (APS)
Date: 15-05-1999
Publisher: Optica Publishing Group
Date: 02-03-2023
DOI: 10.1364/BOE.480615
Abstract: Early detection of skin pathologies with current clinical diagnostic tools is challenging, particularly when there are no visible colour changes or morphological cues present on the skin. In this study, we present a terahertz (THz) imaging technology based on a narrow band quantum cascade laser (QCL) at 2.8 THz for human skin pathology detection with diffraction limited spatial resolution. THz imaging was conducted for three different groups of unstained human skin s les (benign naevus, dysplastic naevus, and melanoma) and compared to the corresponding traditional histopathologic stained images. The minimum thickness of dehydrated human skin that can provide THz contrast was determined to be 50 µm, which is approximately one half-wavelength of the THz wave used. The THz images from different types of 50 µm-thick skin s les were well correlated with the histological findings. The per-s le locations of pathology vs healthy skin can be separated from the density distribution of the corresponding pixels in the THz litude–phase map. The possible THz contrast mechanisms relating to the origin of image contrast in addition to water content were analyzed from these dehydrated s les. Our findings suggest that THz imaging could provide a feasible imaging modality for skin cancer detection that is beyond the visible.
Publisher: IEEE
Date: 05-2007
Publisher: IEEE
Date: 09-2008
Publisher: American Chemical Society (ACS)
Date: 10-02-2017
Publisher: The Optical Society
Date: 25-01-2018
DOI: 10.1364/PRJ.6.000117
Publisher: AIP Publishing
Date: 15-11-2010
DOI: 10.1063/1.3514549
Abstract: We investigate the effect of the arsenic source (As2 and As4) on the optical properties of InGaAs quantum rods (QRs) grown by molecular beam epitaxy. Owing to differences in the In and Ga diffusion lengths under As2 and As4 fluxes, photoluminescence (PL) peak energies of the QR s les depend strongly on the As source when similar growth conditions are used. A marked improvement in the PL intensities from QR s les grown using As4 is achieved. However, for both As2 and As4, an increase of the As overpressure results in a PL intensity degradation, probably due to the formation of nonradiative recombination centers.
Publisher: IEEE
Date: 08-2015
Publisher: AIP Publishing
Date: 27-09-2010
DOI: 10.1063/1.3496035
Abstract: We report the design and performance of GaAs/Al0.15Ga0.85As terahertz quantum cascade lasers with double-phonon resonant depopulation and a vertical lasing transition. Devices were processed into gold-clad double-metal waveguides. Lasing at 3 THz was observed up to a heat-sink temperature of 172 K, which compares favorably with the performance of single-phonon resonant depopulation devices based on vertical lasing transitions. These results demonstrate that terahertz quantum cascade lasers based on double-phonon depopulation designs may be a viable alternative to single-phonon depopulation designs for achieving high-temperature operation.
Publisher: Optica Publishing Group
Date: 2008
DOI: 10.1364/OE.16.003242
Abstract: We report terahertz quantum cascade lasers operating in pulsed mode at an emission frequency of 3 THz and up to a maximum temperature of 178 K. The improvement in the maximum operating temperature is achieved by using a three-quantum-well active region design with resonant-phonon depopulation and by utilizing copper, instead of gold, for the cladding material in the metal-metal waveguides.
Publisher: IEEE
Date: 09-2013
Publisher: SPIE
Date: 06-09-2019
DOI: 10.1117/12.2530727
Publisher: IEEE
Date: 10-2019
Publisher: Institution of Engineering and Technology (IET)
Date: 06-2015
DOI: 10.1049/EL.2015.1137
Publisher: Wiley
Date: 07-2017
Publisher: Springer Science and Business Media LLC
Date: 2008
DOI: 10.1186/JBIOL62
Publisher: Springer Science and Business Media LLC
Date: 09-02-2023
DOI: 10.1038/S41467-023-36418-Y
Abstract: Topological cavities, whose modes are protected against perturbations, are promising candidates for novel semiconductor laser devices. To date, there have been several demonstrations of topological lasers (TLs) exhibiting robust lasing modes. The possibility of achieving nontrivial beam profiles in TLs has recently been explored in the form of vortex wavefront emissions enabled by a structured optical pump or strong magnetic field, which are inconvenient for device applications. Electrically pumped TLs, by contrast, have attracted attention for their compact footprint and easy on-chip integration with photonic circuits. Here, we experimentally demonstrate an electrically pumped TL based on photonic analogue of a Majorana zero mode (MZM), implemented monolithically on a quantum cascade chip. We show that the MZM emits a cylindrical vector (CV) beam, with a topologically nontrivial polarization profile from a terahertz (THz) semiconductor laser.
Publisher: IEEE
Date: 2002
Publisher: American Physical Society (APS)
Date: 15-03-1995
Publisher: IEEE
Date: 07-2019
Publisher: Optica Publishing Group
Date: 19-10-2009
DOI: 10.1364/OE.17.019926
Publisher: IEEE
Date: 09-2010
Publisher: The Optical Society
Date: 02-05-2018
DOI: 10.1364/OL.43.002225
Publisher: IEEE
Date: 2006
Publisher: The Optical Society
Date: 07-11-2013
Publisher: IEEE
Date: 2001
Publisher: IEEE
Date: 08-2017
Publisher: Proceedings of the National Academy of Sciences
Date: 15-12-2014
Abstract: As powerful semiconductor laser sources open up new possibilities for the realization of compact and versatile spectroscopy and detection systems, monolithic control of the laser output characteristics becomes essential. Whereas engineering of spectral characteristics and beam shape has reached a high level of maturity, manipulation of the polarization state remains challenging. We present a method for monolithic control of the degree of circular polarization by aperture antennas forming a surface-emitting grating on a semiconductor laser cavity and demonstrate its realization for a terahertz quantum cascade laser. Our approach is not limited to the terahertz regime and paves the way to an increased functionality and customizability of monolithic laser sources for a variety of applications (e.g., vibrational circular dichroism spectroscopy).
Publisher: American Physical Society (APS)
Date: 24-07-2002
Publisher: Springer Science and Business Media LLC
Date: 02-02-2017
DOI: 10.1038/SREP41872
Abstract: The ability to isolate specific, viable cell populations from mixed ensembles with minimal manipulation and within intra-operative time would provide significant advantages for autologous, cell-based therapies in regenerative medicine. Current cell-enrichment technologies are either slow, lack specificity and/or require labelling. Thus a rapid, label-free separation technology that does not affect cell functionality, viability or phenotype is highly desirable. Here, we demonstrate separation of viable from non-viable human stromal cells using remote dielectrophoresis, in which an electric field is coupled into a microfluidic channel using shear-horizontal surface acoustic waves, producing an array of virtual electrodes within the channel. This allows high-throughput dielectrophoretic cell separation in high conductivity, physiological-like fluids, overcoming the limitations of conventional dielectrophoresis. We demonstrate viable/non-viable separation efficacy of % in pre-purified mesenchymal stromal cells, extracted from human dental pulp, with no adverse effects on cell viability, or on their subsequent osteogenic capabilities.
Publisher: The Optical Society
Date: 06-03-2015
DOI: 10.1364/OE.23.006915
Publisher: Institution of Engineering and Technology (IET)
Date: 10-2015
DOI: 10.1049/EL.2015.2878
Publisher: IEEE
Date: 08-2015
Publisher: IEEE
Date: 08-2015
Publisher: IEEE
Date: 08-2015
Publisher: IEEE
Date: 08-2015
Publisher: The Optical Society
Date: 30-06-0003
DOI: 10.1364/OL.40.000950
Publisher: IOP Publishing
Date: 15-03-2004
Publisher: The Optical Society
Date: 11-11-2016
DOI: 10.1364/OE.24.026986
Publisher: Elsevier BV
Date: 03-2002
Publisher: IEEE
Date: 08-2015
Publisher: IEEE
Date: 05-2011
Publisher: Springer Science and Business Media LLC
Date: 31-05-2011
Publisher: Wiley
Date: 16-12-2020
Publisher: IEEE
Date: 2001
Publisher: The Optical Society
Date: 29-08-2016
DOI: 10.1364/OE.24.020554
Publisher: Elsevier BV
Date: 12-1998
Publisher: AIP
Date: 2005
DOI: 10.1063/1.1994718
Publisher: SPIE
Date: 27-04-2007
DOI: 10.1117/12.719283
Publisher: IEEE
Date: 08-2015
Publisher: IEEE
Date: 09-2010
Publisher: IEEE
Date: 09-2018
Publisher: AIP
Date: 2011
DOI: 10.1063/1.3666407
Publisher: IOP Publishing
Date: 28-06-2005
DOI: 10.1088/0031-9155/50/14/001
Abstract: S les of cortical bone, derived from human femur, have been studied using terahertz time-domain transmission spectroscopy. The relationship between the broadband THz parameters and the previously acquired values of Young's modulus and x-ray attenuation (CT number), and the density of each bone s le, is investigated. The only significant correlation is that between THz transmission and s le density, suggesting that the potential use of THz radiation as a non-invasive probe of bone quality is limited. The spectra of absorption coefficient and refractive index are plotted over the frequency range 0.1-1.25 THz. There is evidence that the s le hydration state is a factor in the resultant THz parameters.
Publisher: OSA
Date: 2014
Publisher: IEEE
Date: 05-2011
Publisher: Institution of Engineering and Technology (IET)
Date: 06-2017
DOI: 10.1049/EL.2017.0662
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2020
Publisher: OSA
Date: 2015
Publisher: AIP Publishing
Date: 07-10-2003
DOI: 10.1063/1.1619223
Abstract: Terahertz radiation was generated with a biased and asymmetrically excited low-temperature-grown GaAs photoconductive emitter, and characterized with a 20-μm-thick ZnTe crystal using free-space electro-optic s ling. Using a backward collection scheme, we obtained terahertz radiation with frequency components over 30 THz, the highest ever observed for photoconductive emitters. We present spectra over the whole frequency range between 0.3 and 20 THz, demonstrating the use of this source for ultrabroadband THz spectroscopy.
Publisher: OSA
Date: 2014
Publisher: Elsevier BV
Date: 12-1998
Publisher: AIP Publishing
Date: 03-11-2008
DOI: 10.1063/1.3013349
Abstract: We demonstrate that terahertz microstrip-line waveguides can be used to measure absorption spectra of polycrystalline materials with a high frequency resolution (∼2 GHz) and with a spatial resolution that is determined by the microstrip-line dimensions, rather than the free-space wavelength. The evanescent terahertz-bandwidth electric field extending above the microstrip line interacts with, and is modified by, overlaid dielectric s les, thus enabling the characteristic vibrational absorption resonances in the s le to be probed. As an ex le, the terahertz absorption spectrum of polycrystalline lactose monohydrate was investigated the lowest lying mode was observed at 534(±2) GHz, in excellent agreement with free-space measurements. This microstrip technique offers both a higher spatial and frequency resolution than free-space terahertz time-domain spectroscopy and requires no contact between the waveguide and s le.
Publisher: AIP Publishing
Date: 10-04-2000
DOI: 10.1063/1.126247
Publisher: IEEE
Date: 10-2017
Publisher: IOP Publishing
Date: 04-2007
Publisher: Elsevier BV
Date: 07-1994
Publisher: Springer Science and Business Media LLC
Date: 2005
Publisher: AIP Publishing
Date: 21-12-2020
DOI: 10.1063/5.0033367
Abstract: We demonstrate a high-temperature performance quantum detector of Terahertz (THz) radiation based on three-dimensional metamaterial. The metamaterial unit cell consists of an inductor-capacitor (LC) resonator laterally coupled with antenna elements. The absorbing region, consisting of semiconductor quantum wells, is contained in the strongly ultra-subwavelength capacitors of the LC structure. The high radiation loss of the antenna allows strongly increased collection efficiency for the incident THz radiation, while the small effective volume of the LC resonator allows intense light-matter coupling with a reduced electrical area. As a result, our detectors operate at much higher temperatures than conventional quantum well detectors demonstrated so far.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2012
End Date: 2013
Funder: European Space Agency
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Funder: Royal Society
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Funder: Royal Society
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Funder: Engineering and Physical Sciences Research Council
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End Date: 2015
Funder: Wellcome Trust
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Funder: Engineering and Physical Sciences Research Council
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Funder: Research Executive Agency
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Funder: Home Office
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Funder: Engineering and Physical Sciences Research Council
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Funder: Biotechnology and Biological Sciences Research Council
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Funder: European Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: UK Research and Innovation
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Funder: UK Research and Innovation
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Funder: UK Space Agency
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: European Commission
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: European Commission
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Funder: European Commission
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Funder: European Commission
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Funder: Engineering and Physical Sciences Research Council
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Funder: Leverhulme Trust
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Funder: National Institute for Health Research
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Funder: Engineering and Physical Sciences Research Council
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