Abstract

Because of its simplicity and accuracy the Z-scan method became a widely used standard routine for studying the nonlinear index of refraction, n₂, and the nonlinear absorption coefficient, β. By scanning the sample longitudinally around the focal plane of a focused Gaussian beam and monitoring the on-axis far-field intensity a sensitive measurement of n₂ and β is possible. Most Z-scan theories are valid either in the thin-sample limit [1,2] or in the limit of small nonlinearity [3]. In this work, a nonlinear paraxial wave equation (NPWE) was derived that describes the beam propagation in a medium having nonlinear refraction and absorption. Furthermore, a numerical algorithm was developed for solving the NPWE in a medium with arbitrary thickness and nonlinearity [4]. The intensity distribution behind the sample is determined by the Huygens-Fresnel principle, thereby completing our general Z-scan theory.

© 2009 IEEE