Nonlinear optical properties in bulk semi-insulating GaAs probed by picosecond pulses

We have characterized through degenerate four wave mixing (DFWM) the nonlinear optical response of bulk GaAs at =1.O64 um. At the lower intensities, for the compensated samples, the reflectivity is accounted by a 3rd order nonlinearity, mainly due to free carrier generation, with a decay time of 1 ns. From high intensity data we derive for all samples a two photon absorption coefficient in agreement with the most recent reported values