Ultralow residual reflectance ZnS substrate long wave antireflection film

Abstract

The invention discloses an ultralow residual reflectance ZnS substrate long wave antireflection film. The antireflection film is characterized by being combined with three kinds of film material including germanium, zinc sulfide and yttrium fluoride, and the total physical thickness of the antireflection film is controlled within 2 micrometer. There are two layers of the yttrium fluoride film with high stress; the thickness of a larger yttrium fluoride film layer is less than 0.4 micrometer. By coating the antireflection film, the maximum residual reflectance of ZnS substrate at wave band of 7.5-9.7 micrometer can be lowered to below 0.5%, the average reflectance is lowered to below 0.1%. The antireflection film is applicable to all kinds of antireflection treatment for surface of zinc sulfide substrate and can be prepared by various sedimentation methods of thermal evaporation.

Description

technical field [0001] The invention belongs to the technical field of optical films, in particular to the anti-reflection film technology on the surface of optical elements, and relates to a ZnS base long-wave anti-reflection film with ultra-low residual reflectivity. Background technique [0002] Zinc sulfide material has good light transmission characteristics in the 3-5um and 8-12um wave bands, especially in the range of 8-12um, compared with other infrared optical materials except diamond, it has high mechanical strength, high hardness, good refraction It is one of the preferred materials for optical windows of infrared imaging and detection optical systems such as missiles and aircraft pods due to its low temperature coefficient of rate and strong resistance to rain corrosion. Due to the high refractive index of zinc sulfide material (~2.2), the single-sided residual reflectance reaches ~14%. The method of using broadband optical anti-reflection film can solve the prob...

AI Technical Summary

Problems solved by technology

This method cannot meet the requirements of bandwidth and ultra-low residual reflectivity at the same time

2) Non-regular design uses multi-layer film for optimal design, based on numerical optimization method to optimize the physical thickness of multi-layer film according to the target of residual reflectivity, this method is generally used in the design of broadband anti-reflection film; 3) non-uniform film The design is to use the method of continuously changing the refractive index to realize the transition from the substrate refractive index to the air refractive index, but this method has high requirements for the preparation technology and is still immature

The average residual reflectance value of zinc sulfide surface reported at present is generally 0.5%, and the broadband anti-reflection film with residual reflectance lower than 0.2% has not been reported.

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