薄膜光学常数的精确测定对于设计和制备多层薄膜具有重要意义。在JGS1型熔融石英基底上，采用热蒸发沉积方法制备了不同厚度的LaF3单层薄膜样品，利用光度法来获取弱吸收薄膜和基底的光学常数，计算得到其在185~450 nm范围内折射率n和消光系数k的色散曲线。实验结果表明，当膜层厚度较薄时，LaF3薄膜折射率表现出不均匀性现象。随着薄膜厚度的增加，薄膜折射率不均匀性减小。在求解过程中选用不均匀模型后，拟合结果与实际测试光谱曲线吻合得很好，提高了薄膜光学常数的计算精度。

To obtain the precise optical constants of thin films, LaF3 thin films of different thickness are deposited by Mo-boat evaporation on fused silica (JGS1). A model for extracting the optical constants of weak absorbing film is applied, which is based on spectrophotometry. The refractive index n and extinction coefficients k of the thin films and substrate are obtained in the range of 185~450 nm. It is found that the refractive index inhomogeneity of LaF3 thin films decreases as the film thickness becomes thick. The calculated optical performances curves fits the experimental ones well when the inhomogeneous model is employed, which can improve the precision of thin film′s optical constants determination.