Nondegenerate two-photon absorption in GaSb

The nonlinear optical absorption of n-type GaSb at 77 K was investigated using time-resolved pump-probe techniques. By holding the pump wavelength constant and varying the probe wavelength, the nondegenerate two-photon absorption spectrum was measured for parallel and perpendicular polarization orientations between the pump and probe beams. The nondegenerate two-photon absorption coefficients, which were measured to be as large as 140 cm/GW, are found to be 2-3 times smaller for the perpendicularly polarized case than in the parallel polarization case. A Kramers-Krönig transformation allowed the determination of the dispersion of the nondegenerate nonlinear refractive index, which was found to be as large as 2×10−3 cm2/GW.