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KMID : 1159320120140030263
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Korean Journal of Vision Science
2012 Volume.14 No. 3 p.263 ~ p.270
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The Fabrication and Characteristics for Infrared bandpass filter deposited by Ge, ZnS multilayer on Al2O3 substrate
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Park Moon-Chan
Kim Dea-Jong
Ko Kyun-Chae
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Abstract
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Purpose : The mid-infrared bandpass filters with a 3450nm central wavelength of 95% transmittance and 150nm FWHM using Ge/ZnS mutilayer were fabricated on Al2O3 substrate, and their characteristics were studied.
Method : In design of the mid-infrared bandpass filters, one surface and the other surface on Al2O3 substrate was composed of longwave-pass filter, and shortwave-pass filter, respectively. IR filters were made by electron beam evaporation apparatus and the transmittaces of the filters were measured by FTIR. The structures of IR filters were assessed by XRD patterns and the compositions of filters were analysed with XPS.
Results : The optimization for the longwave-pass filter at reference wavelength of 2700nm was [air/0.490H 0.904L 0.952H 1.086L 1.747H 0.489L (HL)9 H 0.350L 1.616H/Al2O3 substrate], in which the high and low refractive materials are Ge and ZnS, respectively. The optimization for the short-pass filter at reference wavelength of 4200nm was [air/1.261H (LH)7 0.921L 1.306H/Al2O3 substrate], in which the high and low refractive material are the same as the materials of longwave-pass filter. IR filters were fabricated on the basis of simulation data, of which the peak of the maximun transmittance was shifted to the right of about 30nm wavelength when compared with simulation data. It was known that ZnS thin film has a cubic structure with a (111) crystal surface and the structure of Ge thin film was amorphous from XRD patterns of the filter, and Ge layer was deposited on top of Ge/ZnS mutilayer and the filter was consisted of alternating layers of
Ge and ZnS layer from XPS analysis of IR filters.
Conclusions : One surface and the other surface of IR filter using alterating layer of Ge and ZnS were designed for longwave-pass filter, and shortwave-pass filter, respectively. The infrared bandpass filters with a 3450nm central wavelength of 95% transmittance and 150nm FWHM were fabricated on Al2O3 substrate.
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KEYWORD
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ZnS multilayer, IR pass filter, Longwave-pass filter, shortwave-pass filter
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