几种氟化物薄膜材料的光学特性

Optical properties of several fluoride materials

为了进一步明确氟化薄膜材料在紫外(UV)-真空紫外(VUV)波段的光学常数,研究了真空紫外领域常用的基底材料和6种大带隙的氟化物薄膜材料的光学特性。分别在熔石英(JGS1)基底和氟化镁单晶基底上用热舟蒸发法以不同的沉积速率和不同的基底温度镀制了3种高折射率材料薄膜LaF3、NdF3、GdF3和3种低折射率材料薄膜MgF2、AlF3、Na3AlF6;在国家同步辐射真空紫外实验站测定了它们120～300nm的透射光谱曲线,用商用lambda900光谱仪测量了它们190～500nm的透射光谱曲线,两者相结合标定了透射率的准确值。用包络法和模拟退火相结合研究了它们在120～500nm的折射率和消光系数,给出了6种氟化物材料的光谱色散曲线。结果显示,3种高折射率薄膜的折射率在157nm处约为1.77～1.89,而3种低折射率薄膜的折射率在157nm处约为1.44～1.48;研究表明,选用折射率相差较大的高、低折射率氟化物薄膜,可在膜系设计中组成高低折射率材料对,用于设计各种实用的薄膜器件。

Several kind of wide band-gap fluoride materials are studied to determine optical constants of fluoride films in deep ultraviolet（VUV） to ultraviolet（UV）. High-refractive-index materials LaF3, NdF3, and GdF3 and low-refractive-index materials MgF2, AlF3, and Na3 AlF6 single thin films are deposited by a resistive-heating boat on JGS1 and single crystal MgF2 substrates respectively at different deposited rates and specific substrate temperatures. Transmittances of all fluoride thin films are measured through a commercial spectrometer in the ambient atmosphere and wavelength regions from 190 nm to 500 nm,and measured through synchrotron radiation under vacuum in the wavelength regions from 120 nm to 300 nm. The optical constants of these materials are determined by a envelope method and a simulated annealing method,which matches the calculated and measured values of the transmittance. Measured results indicate that the refractive indexes are about 1.77-1.89 at 157 nm for LaF3, NdF3, and GdF3 single layer films, and are about 1.44- 1. 48 at 157 nm for MgF2, AlF3, and Na3AlF6 single layer films. Experiments show also that these high and low index materials can be eomposited to material pairs to design and manufacture the cost-effective, mechanically and optically stable optical coatings in 120 nm to 500 nm for new thin devices.