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把GeC/GaP双层膜用作ZnS衬底的长波红外(8~11.5μm波段)增透保护膜系。采用射频磁控溅射法,以高纯Ar为工作气体、单晶GaP圆片为靶制备了GaP薄膜;用射频磁控反应溅射法在高纯Ar和CH4的混合气体中,以单晶Ge圆片为靶制备了GeC薄膜。分别用柯西(Cauchy)公式和乌尔巴赫(Urbach)公式表示折射率和吸收系数,对薄膜的红外透射率曲线进行最小二乘法拟合,得到了它们的厚度及折射率、吸收系数等光学常数。GaP膜的折射率与块体材料的相近,在波长10μm处约为2.9;GeC膜的折射率较小,在波长10μm处约为1.78。用所得到的薄膜折射率,通过计算机膜系自动设计软件在ZnS衬底上设计并制备出了GeC/GaP双层增透保护膜系,当GaP膜厚较大时,由于吸收增大膜系增透效果较差;当GaP膜厚较小时,膜系有较好的增透效果。
The GeC / GaP bilayer film is used as a long wave infrared (8-11.5 μm band) AR coating system for ZnS substrates. The GaP film was prepared by radio frequency magnetron sputtering method using high-purity Ar as working gas and single-crystal GaP wafer as targets. In the mixed gas of high-purity Ar and CH4, single-crystal Ge wafer for the preparation of GeC film. The Cauchy and Urbach formulas were used respectively to represent the refractive index and the absorption coefficient. The infrared transmittance curves of the films were fitted by the least square method. Their thickness and refractive index, absorption coefficient and other optical properties constant. The refractive index of the GaP film is similar to that of the bulk material and is about 2.9 at a wavelength of 10 μm; the refractive index of the GeC film is small, about 1.78 at a wavelength of 10 μm. Using the refractive index of the obtained film, the GeC / GaP double-layer antireflection coating was designed and prepared on the ZnS substrate by computerized film automatic design software. When the GaP film thickness is larger, Antireflecting effect is poor; when the GaP film thickness is small, the film system has a better antireflection effect.