Abstract

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 ${\mathrm{As}}_2{\mathrm{S}}_3$ thin film by measuring the Z-scan transmittance with both open and closed apertures. The nonlinear refractive index $\gamma =7.6\times {10}^{-5} {\mathrm{cm}}^2/\mathrm{W}$ and the nonlinear absorption coefficient $\beta =1.6 \mathrm{cm}/\mathrm{W}$ of ${\mathrm{As}}_2{\mathrm{S}}_3$ were measured at subbandgap 633-nm illumination.

© 1999 Optical Society of America

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