This paper focused on the method to determine the physical thickness of a single-layer MgF2 film and its refractive index in the deep ultraviolet/vacuum ultraviolet spectral ranges. The single-layer MgF2 film was prepared on the B270 substrate by a Mo boat evaporation method. On the basis of reflectance spectra of the single-layer MgF2 film at various incidence angles, the refractive index and thickness of the film in 170 — 260 nm were determined by the simulated annealing algorithm and were compared with those of determined by ellipsometry. Experimental results indicate that the thicknesses of the MgF2 film are 248. 5 nm and 249. 5 nm by the simulated annealing algorithm and ellipsometry, respectively, which shows a deviation of 0. 4%. Moreover, the refractive indexes of the MgF2 film at 240 — 260 nm obtained by two method mentioned above show a deviation less than 0. 003. Obtained results prove that the method employing the reflectance spectral and simulated annealing is reliable for determining the refractive index and thickness of the MgF2 film.%研究了确定单层MgF2薄膜的物理厚度及其在深紫外/真空紫外波段折射率的方法.首先,利用钼舟热蒸发工艺在B270基底上制备了单层MgF2薄膜.然后,依据MgF2单层膜在不同入射角下的反射光谱,采用模拟退火方法确定了MgF2薄膜在170～260 nm波段的折射率和物理厚度,并与由椭圆偏振法确定的薄膜参数进行了比较.实验显示,采用模拟退火和椭圆偏振两种方法确定的MgF2薄膜厚度分别为248.5 nm和249.5 nm,偏差为0.4％；而用上述两种方法在240～260 nm波段确定的单层MgF2薄膜的折射率偏差均小于0.003.得到的结果证实了依据不同入射角下的反射光谱,用模拟退火方法确定MgF2薄膜厚度和折射率的可靠性.
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