采用一种相对简单而又精确的光度法来计算弱吸收基底上弱吸收薄膜的光学常数, 为低损耗紫外薄膜的设计与实现提供了理论基础。采用JGS1型熔融石英基底, 制备了MgF2与LaF3材料的单层膜, 获得了JGS1型熔融石英基底及MgF2与LaF3薄膜的光学常数色散曲线。结果显示：在200 nm左右处, JGS1型熔融石英基底的吸收已经比较明显, 消光系数在10-8量级, 因此, 应考虑基底的弱吸收, 以提高薄膜光学常数的计算精度。

A relatively simple and accurate photometric method was presented to calculate the optical constants of the weak absorption coatings on weak absorotion substrate materials . And the optical constants of the JGS1 fused silica substrate, MgF2 and LaF3 films were calculated according to the above method. The results show that, at the wavelength of 200 nm, the absorption of the JGS1 fused silica substrate is relatively obvious with the extinction coefficient of 10-8 level. Therefore, the weak absorption of the substrate should be taken into account to improve the calculation precision of the film’s optical constants.