STRAIHGHTFORWARD REPRESENTATION OF A THICK NONLINEAR OPTICAL MATERIAL, WITH LINEAR AND NONLINEAR ABSORPTION

Z-scan is a technique where a thin sample with good optical quality is scanned through the focus of a gaussian laser beam. A sensor is placed behind a finite aperture in the far field to monitor the output from the sample. A further simplification is obtained measuring transmission only when the sample is close to the focal point, and the aperture is small. In this work. z-scan like results are obtained when a nonlinear optical material is modeled as a set of spherical lenses using geometric optics. Here we discus the thick sample case; sample thicker than the confocal length (defined by the external lens) or samples with nonlinear phase change appreciably different from zero. An absorbent material with instantaneous nonlinear response will be used. With this procedure, an explanation for the distortion in the z-scan is obtained with the increase in the aperture, the nonlinear refractive index and the sample thickness as well as with the presence of nonlinear absorption.