Picosecond pump-probe technique to measure deep-level, free-carrier, and two photon cross sections in GaAs

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Abstract
Optical transmission of a weak probe pulse in the presence of a strong cross-polarized pump pulse is measured as a function of pump-probe delay. We use pulses of duration 35 ps at a wavelength of 1.06 μm and two samples of undoped, semi-insulating GaAs cut from two dissimilar boules. Numerical solutions to the rate equations coupled with the nonlinear wave equation for propagation in GaAs are fit to the experimental results in order to determine rate coefficients. We obtain a two-photon absorption coefficient of 27±5 cm/GW, a free-carrier cross section (5.5±2)×10−18 cm2, and the ratio of the hole cross section to the electron cross section for the EL2 defect 0.76±0.1.