纵向扫描法测量非线性折射率和吸收的理论分析和测量结果

本文以薄样品的分析为基础,采用高斯分解方法,在一定近似条件下,对纵向扫描进行严格的理论推导,获得了远场光阑归一化透过率的数值解析表达式.利用所得表达式,由测得的归一化透过率曲线可同时获得非线性折射率和非线性吸收的大小和符号.对非线性吸收和极值点的讨论进一步证明了结果的准确性.最后简要介绍了一种自行设计的全自动纵向扫描测试系统,并对CS₂标准样品进行了闭孔测量.测得CS₂的非线性折射率大小与国际报道完全一致.

THEORETICAL ANALYSIS AND EXPERIMENTAL RESULT OF Z-SCAN FOR MEASUREMENTS OF NONLINEAR REFRACTION AND ABSORPTION

Using Gaussian decomposition method,we theoretically analyzed Z-scan in thin sample and derived a numerical analytical expression of the normalized z-scan transmittance in far-field aperture, including nonlinear absorption.Based on the expression,after a Z-scan is performed the nonlinear index and nonlinear absorption were readily and simultaneously evaluated.Useful discussions on the expression for nonlinear absorption and extreme point indicated that it is more accurate and simple than other’s.Finally,we showed an automatic Z-scan experimental system.The value of nonlinear refractive index,n₂ for CS₂ measured on the system was(1.2±0.2)×10^-11esu,is fairly consistent with the repoted values.