Nonlinear optical studies of picosecond relaxation times of electrons in n-GaAs and n-GaSb

The third order nonlinear optical susceptibility of free carriers has been studied in n-GaAs and n-GaSb as a function of the frequency difference δω between two Q-switched CO2 laser beams for different lattice temperatures. The nonlinear response of the electron gas results from the modulation of the carrier mass as the kinetic energy and electron distribution are driven at frequency δω. This modulation arises both from the nonparabolicity of the light mass Γ minimum and, at high temperatures, from the transfer of electrons between the Γ and the heavier mass L minima. The frequency dependence of the response yields the intervalley and energy relaxation times.