Analysis of asymmetric Z-scan measurement for large optical nonlinearities in an amorphous As2S3 thin film

We have extended the conventional Z-scan theory by employing an aberration-free approximation of a Gaussian beam through a nonlinear medium and derived a simple analytical formula for Z-scan transmittance, including the effects of both nonlinear absorption and nonlinear refraction, which could be applicable to the sample with large nonlinear phase shifts. We verified the extended Z-scan theory in an amorphous chalcogenide As2S3 thin film by measuring the Z-scan transmittance with both open and closed apertures. The nonlinear refractive index gamma = 7.6 x 10(-5) cm(2)/W and the nonlinear absorption coefficient beta = 1.6 cm/W of As2S3 were measured at subbandgap 633-nm illumination. (C) 1999 Optical Society of America [S0740-3224(99)01304-1] OCIS codes: 190.3270, 190.5940, 090.4720, 160.4330, 160.2750.