角度对KDP晶体非线性光学参数的影响研究

Investigation on Nonlinear Optical Parameters for Different Orientations of KDP Crystal

采用传统溶液降温法生长了KDP晶体，利用单光束Z扫描技术对不同取向的KDP晶体在λ=532nm条件下的非线性折射和非线性吸收性质进行了研究；在皮秒激光脉冲条件下，以KDP晶体的应用为基础，探讨角度与KDP晶体非线性光学参数的关系。在本实验条件下，KDP晶体具有明显的非线性折射现象，而无明显非线性吸收现象，表现出明显的自聚焦效应。相关理论计算得到KDP晶体的非线性折射率γ（n2）和相应的三阶非线性极化率χk（3）。结果表明：样品的取向对KDP晶体的非线性光学参数γ（n2），χk（3）的数值具有一定的影响；在相位匹配方向（Ⅰ类和Ⅱ类）具有相对较小的非线性光学系数。

KDP crystal is grown by the traditional temperature lowering method. From the perspective of orientations, nonlinear refraction and nonlinear absorption for KDP crystal are performed by the single Z-scan method at the wavelength of 532 nm. Based on the application of the KDP crystal, the relationship between nonlinear optical parameters and direction has been proved in the picosecond laser pulse. Under the experimental conditions, it is shown that nonlinear refraction can be clearly observed, but no obvious nonlinear absorption phenomena. Self- focusing effect has been discovered in KDP crystal. Then, nonlinear refractive index γ（n2 ） and nonlinear susceptibility χk（3） are calculated through the relative theory. The results show that the nonlinear optical parameters γ（n2 ）andχk（3） for KDP crystals can be affected by orientations, and the values are small for phase-matching directions （Ⅰ and Ⅱ types）.