Analysis of asymmetric Z-scan measurement for large optical nonlinearitiesin 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 derive d a simple analytical formula for Z-scan transmittance, including the effec ts of both nonlinear absorption and nonlinear refraction, which could be ap plicable to the sample with large nonlinear phase shifts. We verified the e xtended Z-scan theory in an amorphous chalcogenide As2S3 thin film by measu ring the Z-scan transmittance with both open and closed apertures. The nonl inear refractive index gamma = 7.6 x 10(-5) cm(2)/W and the nonlinear absor ption 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.