大尺寸磷酸二氢钾晶体的折射率均一性研究

采用德国Trioptics公司生产的新一代全自动高精度折射率测量仪,测量了磷酸二氢钾(KDP)晶体不同部位的样品位于近紫外到近红外波段(0.253—1.530μm)内12个不同波长处的折射率,测量精度达到10-6量级.结果表明,大尺寸KDP晶体不同部位样品的折射率存在不均一性,靠近晶体恢复区的样品折射率小于晶体锥头区的样品折射率,偏差在10-5—10-4量级.研究发现,这种折射率不均一性与晶体不同部位的结晶质量存在差异有关.另外,将测量数据与其他文献中的数据进行对比.结果显示,所测试的样品数、波段宽度、测量点数量以及数据的精度均超过其他文献,结合测试条件分析了不同文献数据存在差异的原因.最后,使用最小二乘法拟合得到了KDP晶体较为可靠的Sellmeier方程.

Refractive index homogeneity of large scale potassium dihydrogen phosphate crystal

By using a traditional temperature reduction method, a large scale potassium dihydrogen phosphate (KDP) crystal is prepared. The refractive indices of different parts of this as-grown crystal are measured at 12 wavelengths between 0.253 and 1.530 um by using the new generation measuring instrument with an accuracy of 10^-6. The measurement results show that refractive indices are inhomogenous in different parts of the large scale KDP crystal. The refractive index of the selected part close to the recovery area of crystal is smaller than that of selected part far from the recovery area. The deviation is on the order of 10^-5-10^-4. The refractive index inhomogeneity is related to the difference in crystalline quality among different parts in large KDP crystal. Furthermore, our measured data are compared with those in the literature published previously and the difference between them is analyzed. Meanwhile, by using root mean square method, numerical fitting to Sellmeier equation is conducted.
Keywords： potassium dihydrogen phosphate refractive index homogeneity Sellmeier equation