Only recently a rigid quantum-mechanical modeling of free- electron induced optical nonlinearities in highly doped n- GaAs has been elaborated. The total theory takes into account non-parabolicity, hot phonons, effective mass modulation due to (Gamma) -L intervalley transfers, scattering due to equivalent intervalley transfers inside the ellipsoidal L-valleys, nonlinear screening, etc. It was shown that this hot free electron nonlinearity is strongest near the plasma resonance and significantly depends on the deformation potential field (Lambda) _LL describing transitions of L-valley electrons between equivalent L- minima. For the experiments a very sensitive multi-layer leaky waveguide structure for TM polarized waves was designed and grown by MBE. Measurements were performed with 100 ns duration CO₂ laser pulses. For a doping concentration n_o of 7.6 X 10¹⁸cm^-3 a nonlinear refractive index value n₂ equals (1.0 + 0.12)X10^-6 cm²W^-1 at (lambda) equals 10.6 micrometers was obtained, which was based on an experimentally derived (Lambda) _LL equals (1.0 +/- 0.2) X 10⁹ eVcm^-1. With intensities of only several MWcm^-2 more than 50% of the electrons cold be transferred to the L-valleys, leading to impressive absorption increases of more than 50%. With respect to bulk samples the nonlinearity could be more than 20 times increased. In combination with an estimated relaxation time of 6 - 7 ps, this nonlinearity exceeds most other results at room temperature for (lambda) equals 10.6micrometers .

Date Published: 29 May 2002
PDF: 11 pages
Proc. SPIE 4748, ICONO 2001: Fundamental Aspects of Laser-Matter Interaction and Physics of Nanostructures, (29 May 2002); doi: 10.1117/12.468955

Published in SPIE Proceedings Vol. 4748:
ICONO 2001: Fundamental Aspects of Laser-Matter Interaction and Physics of Nanostructures
Anatoly V. Andreev; Pavel A. Apanasevich; Vladimir I. Emel'yanov; Alexander P. Nizovtsev, Editor(s)