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.