MEASURING OPTICAL NONLINEARITIES WITH A 2-BEAM X-SCAN TECHNIQUE

We present a new two-beam technique, the X scan, for measuring both ab sorptive and refractive components of optical nonlinearities in bulk s emiconductors, The sample is excited by a high-intensity, short (picos econd) pump pulse and is probed with weak degenerate or nondegenerate pulses whose relative arrival time and transverse alignment with the p ump are varied. X scans at various delays enable separation of fi ee-c arrier mediated nonlinearities and instantaneous chi((3)) nonlineariti es. Varying the relative pump-probe polarizations yields components of the chi((3)) tensor. We report new values for degenerate (532 nm) and nondegenerate (532; 683 nm) cross-phase-modulation and two-photon-abs orption coefficients for two polarization states and free-carrier abso rption and refractive cross sections at 532 and 683 nm. (C) 1997 Optic al Society of America.