| Visible high transmittance and mid-far infrared high-reflectance filters can be widely used in multi-band scanning spectrometer for satellites,imaging spectrometer and solar energy,etc.They are getting more and more attentions.How to improve its transmittance in the visible region and the reflectivity of mid-far infrared,improve its application in these aspects,more effectively detect the targets in the visible and mid-far infrared bands,and develop its special military applications have become research hotspots.In this paper,the filter with high transmittance in visible region and high reflection in mid-far infrared region was researched and developed.Firstly,the film materials required for depositing the filter were ZnS and Ag was confirmed.Then,the ultra-thin silver films with different thickness were deposited by resistive thermal evaporation deposition.The properties of the ultra-thin silver films were studied by ellipsometry and effective medium theory.The optical constants of the thin silver films were given and the variation laws were analyzed.On this basis,the design,optimization and analysis of the coating system were carried out.The final design of the filter was ZnS(35nm)/Ag(13nm)/ZnS(36nm)using a TFCalc design software.Then,the deposition process of single layer ZnS was studied by electron beam thermal evaporation deposition technology,and the preparation process parameters and thicknesses controlling methods of ZnS thin films were given.Finally;the filters were manufactured,and the transmittance of the filters in the visible region were tested by a ultraviolet-visible-near infrared spectrophotometer,and the reflectance of the filters in the mid-far infrared was measured by a Fourier Transform Infrared spectrometer.The test results show that the average transmittance of the filter Ta,e=87.15%,at 400-700 nm,the maximum transmittance of the filter Tmax=90.53%,and the average reflectance Rave=95.07%,in the range of 3-12 ?m,which meets the design requirements. |
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