ORCID Profile
0000-0001-5565-0463
Current Organisations
University of Leeds
,
University of Leeds Faculty of Engineering
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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: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2020
Publisher: IEEE
Date: 09-2013
Publisher: The Optical Society
Date: 22-04-2014
DOI: 10.1364/OL.39.002629
Publisher: IEEE
Date: 10-2011
Publisher: The Optical Society
Date: 02-05-2018
DOI: 10.1364/OL.43.002225
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: IEEE
Date: 10-2013
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: 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: 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: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2013
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: Institution of Engineering and Technology (IET)
Date: 10-2015
DOI: 10.1049/EL.2015.2878
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: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2020
Publisher: The Optical Society
Date: 27-06-2014
DOI: 10.1364/OE.22.016595
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: IEEE
Date: 09-2019
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: 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: IOP Publishing
Date: 22-08-2012
Publisher: Institution of Engineering and Technology (IET)
Date: 02-2014
DOI: 10.1049/EL.2013.4035
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2013
Publisher: AIP Publishing
Date: 06-2019
DOI: 10.1063/1.5094674
Publisher: IEEE
Date: 09-2012
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 04-2018
Publisher: SPIE
Date: 05-09-2014
DOI: 10.1117/12.2061433
Publisher: Institution of Engineering and Technology (IET)
Date: 06-2015
DOI: 10.1049/EL.2015.1137
Publisher: The Optical Society
Date: 05-02-2018
DOI: 10.1364/OE.26.003814
Publisher: IEEE
Date: 12-2012
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2020
Publisher: The Optical Society
Date: 07-2011
DOI: 10.1364/OL.36.002587
Publisher: The Optical Society
Date: 17-10-2014
DOI: 10.1364/BOE.5.003981
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
No related grants have been discovered for Alexander Valavanis.