ORCID Profile
0000-0002-6746-7110
Current Organisations
Imperial College London
,
Northumbria University
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Publisher: IEEE
Date: 06-2019
Publisher: MDPI AG
Date: 13-04-2021
DOI: 10.3390/S21082751
Abstract: In this paper, we investigate the performance of a vehicular visible light communications (VVLC) link with a non-collimated and incoherent light source (a light-emitting diode) as the transmitter (Tx), and two different optical receiver (Rx) types (a camera and photodiode (PD)) under atmospheric turbulence (AT) conditions with aperture averaging (AA). First, we present simulation results indicating performance improvements in the signal-to-noise ratio (SNR) under AT with AA with increasing size of the optical concentrator. Experimental investigations demonstrate the potency of AA in mitigating the induced signal fading due to the weak to moderate AT regimes in a VVLC system. The experimental results obtained with AA show that the link’s performance was stable in terms of the average SNR and the peak SNR for the PD and camera-based Rx links, respectively with dB SNR penalty for both Rxs, as the strength of AT increases compared with the link with no AT.
Publisher: IEEE
Date: 06-2019
Publisher: The Optical Society
Date: 13-05-2013
DOI: 10.1364/OE.21.012309
Publisher: IEEE
Date: 09-2020
Publisher: Springer Science and Business Media LLC
Date: 20-02-2015
DOI: 10.1038/NCOMMS7215
Abstract: Recently, the world’s first room-temperature maser was demonstrated. The maser consisted of a sapphire ring housing a crystal of pentacene-doped p -terphenyl, pumped by a pulsed rhodamine-dye laser. Stimulated emission of microwaves was aided by the high quality factor and small magnetic mode volume of the maser cavity yet the peak optical pumping power was 1.4 kW. Here we report dramatic miniaturization and 2 orders of magnitude reduction in optical pumping power for a room-temperature maser by coupling a strontium titanate resonator with the spin-polarized population inversion provided by triplet states in an optically excited pentacene-doped p -terphenyl crystal. We observe maser emission in a thimble-sized resonator using a xenon flash l as an optical pump source with peak optical power of 70 W. This is a significant step towards the goal of continuous maser operation.
Publisher: IEEE
Date: 20-07-2020
Publisher: Springer Science and Business Media LLC
Date: 07-02-2017
DOI: 10.1038/SREP41836
Abstract: The performance of a room temperature, zero-field MASER operating at 1.45 GHz has been examined. Nanosecond laser pulses, which are essentially instantaneous on the timescale of the spin dynamics, allow the visible-to-microwave conversion efficiency and temporal response of the MASER to be measured as a function of excitation energy. It is observed that the timing and litude of the MASER output pulse are correlated with the laser excitation energy: at higher laser energy, the microwave pulses have larger litude and appear after shorter delay than those recorded at lower laser energy. Seeding experiments demonstrate that the output variation may be stabilized by an external source and establish the minimum seeding power required. The dynamics of the MASER emission may be modeled by a pair of first order, non-linear differential equations, derived from the Lotka-Volterra model (Predator-Prey), where by the microwave mode of the resonator is the predator and the spin polarization in the triplet state of pentacene is the prey. Simulations allowed the Einstein coefficient of stimulated emission, the spin-lattice relaxation and the number of triplets contributing to the MASER emission to be estimated. These are essential parameters for the rational improvement of a MASER based on a spin-polarized triplet molecule.
Publisher: Springer Science and Business Media LLC
Date: 23-08-2018
DOI: 10.1038/S41598-018-30983-9
Abstract: The multiplexing capacity of conventional fluorescence materials are significantly limited by spectral overlap and background interference, mainly due to their short-lived fluorescence lifetimes. Here, we adopt a novel Gd 3+ doping strategy in NaYF 4 host materials, realized tuning of upconversion photoluminescence (UCPL) lifetimes at selective emissions. Time-correlated single-photon counting (TCSPC), was applied to measure the photoluminescence lifetimes accurately. We demonstrated the large dynamic range of lifetimes of upconversion nanoparticles with good upconversion quantum yields, mainly owing to the dominance of high efficient energy transfer upconversion mechanism. The exceptional tunable properties of upconversion materials allow great potential for them to be utilized in biotechnology and life sciences.
Publisher: Elsevier BV
Date: 03-2018
Publisher: IOP Publishing
Date: 24-10-2013
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2021
Publisher: IEEE
Date: 06-2019
Publisher: Springer Science and Business Media LLC
Date: 28-09-2017
DOI: 10.1038/S41534-017-0041-3
Abstract: The strong coupling regime is essential for efficient transfer of excitations between states in different quantum systems on timescales shorter than their lifetimes. The coupling of single spins to microwave photons is very weak but can be enhanced by increasing the local density of states by reducing the magnetic mode volume of the cavity. In practice, it is difficult to achieve both small cavity mode volume and low cavity decay rate, so superconducting metals are often employed at cryogenic temperatures. For an ensembles of N spins, the spin–photon coupling can be enhanced by $$\\sqrt N$$ N through collective spin excitations known as Dicke states. For sufficiently large N the collective spin–photon coupling can exceed both the spin decoherence and cavity decay rates, making the strong-coupling regime accessible. Here we demonstrate strong coupling and cavity quantum electrodynamics in a solid-state system at room-temperature. We generate an inverted spin-ensemble with N ~ 10 15 by photo-exciting pentacene molecules into spin-triplet states with spin dephasing time $$T_2^*\\sim 3$$ T 2 * ~ 3 μs. When coupled to a 1.45 GHz TE 01δ mode supported by a high Purcell factor strontium titanate dielectric cavity ( $$V_{\\mathrm{m}}\\sim 0.25$$ V m ~ 0.25 cm 3 , Q ~ 8,500), we observe Rabi oscillations in the microwave emission from collective Dicke states and a 1.8 MHz normal-mode splitting of the resultant collective spin–photon polariton. We also observe a cavity protection effect at the onset of the strong-coupling regime which decreases the polariton decay rate as the collective coupling increases.
Publisher: IEEE
Date: 09-2020
Publisher: IEEE
Date: 08-2011
Publisher: Springer Science and Business Media LLC
Date: 19-12-2018
DOI: 10.1038/NATURE25970
Abstract: The maser-the microwave progenitor of the optical laser-has been confined to relative obscurity owing to its reliance on cryogenic refrigeration and high-vacuum systems. Despite this, it has found application in deep-space communications and radio astronomy owing to its unparalleled performance as a low-noise lifier and oscillator. The recent demonstration of a room-temperature solid-state maser that utilizes polarized electron populations within the triplet states of photo-excited pentacene molecules in a p-terphenyl host paves the way for a new class of maser. However, p-terphenyl has poor thermal and mechanical properties, and the decay rates of the triplet sublevel of pentacene mean that only pulsed maser operation has been observed in this system. Alternative materials are therefore required to achieve continuous emission: inorganic materials that contain spin defects, such as diamond and silicon carbide, have been proposed. Here we report a continuous-wave room-temperature maser oscillator using optically pumped nitrogen-vacancy defect centres in diamond. This demonstration highlights the potential of room-temperature solid-state masers for use in a new generation of microwave devices that could find application in medicine, security, sensing and quantum technologies.
Publisher: The Optical Society
Date: 06-2012
DOI: 10.1364/AO.51.003684
Publisher: Beilstein Institut
Date: 25-05-2016
DOI: 10.3762/BJNANO.7.66
Abstract: In this paper we report the design and experimental realisation of a novel refractive index sensor based on coupling between three nanoscale stripe waveguides. The sensor is highly compact and designed to operate at a single wavelength. We demonstrate that the sensor exhibits linear response with a resolution of 6 × 10 −4 RIU (refractive index unit) for a change in relative output intensity of 1%. Authors expect that the outcome of this paper will prove beneficial in highly compact, label-free and highly sensitive refractive index analysis.
Publisher: IEEE
Date: 06-2019
Publisher: IEEE
Date: 13-09-2021
Publisher: The Optical Society
Date: 08-06-2017
DOI: 10.1364/OE.25.013714
Publisher: American Chemical Society (ACS)
Date: 07-04-2016
Publisher: The Optical Society
Date: 12-11-2018
DOI: 10.1364/OE.26.031129
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 15-08-2021
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 15-08-2021
Publisher: Optica Publishing Group
Date: 07-2020
DOI: 10.1364/JOSAB.395394
Abstract: This work presents a study of a fully nonastigmatic design of a single-longitudinal-mode, wavelength-tunable, unidirectional alexandrite ring laser cavity and assessment of its performance compared to more complex laser design requiring astigmatism compensation. A “displaced mode” nonastigmatic laser cavity design eliminating astigmatic cavity elements is developed around an alexandrite crystal end-pumped by a low-brightness, high-power red diode laser pump system. Single-longitudinal-mode, continuous-wave operation is demonstrated with output power of 700 mW with an excellent T E M 00 mode ( M 2 <!-- 1.1 ) across a wide pump power range. Wavelength tuning from 748–773 nm is produced using a birefringent filter plate. The nonastigmatic alexandrite laser design achieves better spatial quality and resilience to maintain T E M 00 operation across wide variation in pump-induced lensing compared to the astigmatic design. To the best of our knowledge, this is the first wavelength-tunable, single-longitudinal-mode operation of a unidirectional alexandrite ring system in a fully nonastigmatic cavity regime.
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 Juna Sathian.