We present a new two-beam technique, the X scan, for measuring both absorptive and refractive components of optical nonlinearities in bulk semiconductors. The sample is excited by a high-intensity, short (picosecond) pump pulse and is probed with weak degenerate or nondegenerate pulses whose relative arrival time and transverse alignment with the pump are varied. X scans at various delays enable separation of free-carrier mediated nonlinearities and instantaneous χ<sup>(3)</sup> nonlinearities. Varying the relative pump–probe polarizations yields components of the χ<sup>(3)</sup> tensor. We report new values for degenerate (532 nm) and nondegenerate (532; 683 nm) cross-phase-modulation and two-photon-absorption coefficients for two polarization states and free-carrier absorption and refractive cross sections at 532 and 683 nm.
© 1997 Optical Society of America
John E. La Sala, Kevin Dietrick, Glenn Benecke, Todd Buhr, David Gardner, Corey Gerving, and Adrian Perica, "Measuring optical nonlinearities with a two-beam X-scan technique," J. Opt. Soc. Am. B 14, 1138-1148 (1997)