| Because of the wide use of the third-order nonlinear optical effects, it is important to search a simple and accurate way to measure the optical nonlinearities of materials. At present, Z-scan technique is widely used. The Z-scan technique is a popular method for measuring optical nonlinearities using a single laser beam. It has the advantage of high sensitivity, but multiple exposure brings about more injury to the sample. In this thesis we present a two-beam interference method based on 4f coherent image system for measurement of third-order optical nonlinearities. Previous 4f coherent imager system which measures third-order nonlinear optical refraction coefficient operates by mean of contrasting the optical intensity on the image plane. This technique can not obtain object wave phase at the image plane. The traditional 4f coherent image system is improved to observe the beam propagation.This thesis is based on the theory of Fourier transform, inverse Fourier transform and nonlinear filtering principle. A two-beam interference method based on 4f coherent image system for measurement of third-order optical nonlinearities is designed. The property of the two-beam interference system is analyzed theoretically. We numerically simulate and sum rules of the interference patterns in the cases of two-photon absorption, nonlinear refraction, nonlinear absorption and refraction coexist. Then phase-shifting digital holography method is used to deduce object wave phase on the image plane. In reconstruction by a computer, we can finally obtain the object wave phase on the incident plane in the two-beam interference system based on 4f coherent imager technique. Contrast the object wave complex amplitude of reconstruction and the real object wave complex amplitude at the incident plane to determine the third-order nonlinear optical coefficient. Define the sign of the third-order nonlinear optical refraction coefficient by observing the center of the interference pattern.
|
PDF Full Text Request