Abstract-An exciton-polariton bolometer for terahertz radiation detection

G. G. Paschos, T. C. H. Liew, Z. Hatzopoulos, A. V. Kavokin, P. G. Savvidis, G. Deligeorgis,

https://www.nature.com/articles/s41598-018-28197-0

We experimentally investigate the feasibility of a bolometric device based on exciton-polaritons. Initial measurements presented in this work show that heating – via thermal expansion and bandgap renormalization – modifies the exciton-polariton propagation wavevector making exciton-polaritons propagation remarkably sensitive to thermal variations. By theoretical simulations we predict that using a single layer graphene absorbing layer, a THz bolometric sensor can be realized by a simple exciton-polariton ring interferometer device. The predicted sensitivity is comparable to presently existing THz bolometric devices with the convenience of being a device that inherently produces an optical signal output.

Abstract-Optically induced transparency in bosonic cascade lasers

T. C. H. Liew and A. V. Kavokin

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-2-259&origin=search

Bosonic cascade lasers are terahertz (THz) lasers based on stimulated radiative transitions between bosonic condensates of excitons or exciton–polaritons confined in a trap. We study the interaction of an incoming THz pulse resonant in frequency with the transitions between neighboring energy levels of the cascade. We show that at certain optical pump conditions the cascade becomes transparent to the incident pulse: it neither absorbs nor amplifies it in the mean-field approximation. The populations of intermediate levels of the bosonic cascade change as the THz pulse passes, nevertheless. In comparison, a fermionic cascade laser does not reveal any of these properties.

© 2018 Optical Society of America

Abstract-Impurity-induced modulation of terahertz waves in optically excited GaAs

A. S. Kurdyubov, A. V. Trifonov, I. Ya. Gerlovin, I. V. Ignatiev, A. V. Kavokin

(Submitted on 11 Jul 2017)

https://arxiv.org/abs/1708.07109

The effect of the photoinduced absorption of terahertz (THz) radiation in a semi-insulating GaAs crystal is studied by the pulsed THz transmission spectroscopy. We found that a broad-band modulation of THz radiation may be induced by a low-power optical excitation in the spectral range of the impurity absorption band in GaAs. The measured modulation achieves 80\%. The amplitude and frequency characteristics of the resulting THz modulator are critically dependent on the carrier density and relaxation dynamics in the conduction band of GaAs. In semi-insulating GaAs crystals, the carrier density created by the impurity excitation is controlled by the rate of their relaxation to the impurity centers. The relaxation rate and, consequently, the frequency characteristics of the modulator can be optimized by an appropriate choice of the impurities and their concentrations. The modulation parameters can be also controlled by the crystal temperature and by the power and photon energy of the optical excitation. These experiments pave the way to the low-power fast optically-controlled THz modulation, imaging, and beam steering.

Abstract-Strong coupling and stimulated emission in single parabolic quantum well microcavity for terahertz cascade

A. Tzimis^1,2, A. V. Trifonov³, G. Christmann², S. I. Tsintzos², Z. Hatzopoulos^2,4, I. V. Ignatiev³, A. V. Kavokin^3,5 and P. G. Savvidis^1,2
 http://scitation.aip.org/content/aip/journal/apl/107/10/10.1063/1.4930165
1 Department of Materials Science and Technology, University of Crete, 71003 Heraklion, Crete, Greece
2 Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, 71110 Heraklion, Crete, Greece
3 Spin Optics Laboratory, State University of Saint-Petersburg, 1 Ulianovskaya, 198504 St. Petersburg, Russia
4 Department of Physics, University of Crete, 71003 Heraklion, Crete, Greece
5 School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, United Kingdom
Appl. Phys. Lett. 107, 101101 (2015); http://dx.doi.org/10.1063/1.4930165

We report observation of strong light-matter coupling in an AlGaAs microcavity (MC) with an embedded single parabolic quantum well. The parabolic potential is achieved by varyingaluminum concentration along the growth direction providing equally spaced energy levels, as confirmed by Brewster angle reflectivity from a reference sample without MC. It acts as an active region of the structure which potentially allows cascaded emission of terahertz (THz) light. Spectrally and time resolved pump-probe spectroscopy reveals characteristic quantum beats whose frequencies range from 0.9 to 4.5 THz, corresponding to energy separation between relevant excitonic levels. The structure exhibits strong stimulated nonlinear emission with simultaneous transition to weak coupling regime. The present study highlights the potential of such devices for creating cascaded relaxation of bosons, which could be utilized for THz emission.

Abstract-Superradiant Terahertz Emission by Dipolaritons

O. Kyriienko1,2, A. V. Kavokin3,4, and I. A. Shelykh1,2 

http://prl.aps.org/abstract/PRL/v111/i17/e176401

1Science Institute, University of Iceland, Dunhagi-3, IS-107 Reykjavik, Iceland
2Division of Physics and Applied Physics, Nanyang Technological University, 637371 Singapore
3School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom
4Spin Optics Laboratory, St. Petersburg State University, Building 1, Ulianovskaya Street, St. Petersburg 198504, Russia

Received 4 November 2012; revised 17 June 2013; published 22 October 2013

Dipolaritons are mixed light-matter quasiparticles formed in double quantum wells embedded in microcavities. Because of resonant coupling between direct and indirect excitons via electronic tunneling, dipolaritons possess large dipole moments. Resonant excitation of the cavity mode by a short pulse of light induces oscillations of the indirect exciton density with a characteristic frequency of Rabi flopping. This results in oscillations of a classical Hertz dipole array which generate supperradiant emission on a terahertz (THz) frequency. The resulting THz signal may be enhanced using the supplementary THz cavity in the weak coupling regime.

© 2013 American Physical Society

Abstract-Polarisation control of optically pumped terahertz lasers

 G. Slavcheva, A. V. Kavokin
http://arxiv.org/abs/1301.6904?context=cond-mat

Optical pumping of excited exciton states in semiconductor quantum wells is a tool for realisation of ultra-compact terahertz (THz) lasers based on stimulated optical transition between excited (2p) and ground (1s) exciton state. We show that the probability of two-photon absorption by a 2p-exciton is strongly dependent on the polarisation of both photons. Variation of the threshold power for THz lasing by a factor of 5 is predicted by switching from linear to circular pumping. We calculate the polarisation dependence of the THz emission and identify photon polarisation configurations for achieving maximum THz photon generation quantum efficiency.