Abstract

Z-scan techniques have been used to measure the nonlinear refractive index and the absorption coefficient of a large number of direct-gap semiconductors, such as GaAs, InSb, CdSe, and ZnSe.^1-3 The origins of the nonlinearities are mainly attributed to two-photon transitions, Raman transitions, the ac Stark shift, and free charge carriers due to two-photon absorption.¹ Picosecond Z-scan and degenerate-four-wave-mixing measurements showed that two-photon transitions, Raman transitions, and the ac Stark shift are the dominant mechanisms for nonlinear refraction up to an irradiance of ~0.5 GW/cm². However, the nonlinearity caused by the two-photon-excited free carriers becomes significant at much higher irradiance levels.¹

© 1995 Optical Society of America