Design and production of antireflection coating for Ge, ZnSe and ZnS in 8-12 micrometer wavelength region

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2009

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Üçer, Begüm

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This thesis describes the works done during the design and deposition process of the antireflection coating for the materials commonly used as refractive optical elements in thermal imaging systems. These coatings are quite necessary to reduce reflection losses from the surface of the optics and stray light that directly affects the image quality. Germanium, zinc sulfide and zinc selenide were used as substrate material and their optical properties were investigated with infrared ellipsometry and FTIR. Antireflection coatings for each material operating in 8-12 μm range were designed with Needle Synthesis Technique. In order to shorten the optimization time, commercial software; “The Essential Macleod” was used. In order to reduce the reflectance losses multilayer structure was used in the coating design, and zinc selenide and lead telluride were used as low and high index materials. In this study the necessary theoretical background and common deposition techniques are reviewed. Samples were produced using the magnetron sputtering. To optimize the v thicknesses of the deposited layers, growth period and rate was controlled. Thicknesses of the samples, following to the deposition were also measured by thickness profilometer. A 3-layer coating, PbTe/ZnSe/PbTe, on ZnS and 2-layer coating PbTe/ZnS on Ge having more than 90% transmittance in 9.7-10.3 μm wavelength region have been successfully produced. Although, the measured range for 3 and 2- layer coating is narrower than the aimed one, it has been shown that, the method developed in this thesis would yield AR-coatings with broader spectral response if a system having better control on deposition parameters is used. For example, our design and optimization work has suggested that a 7-layer AR coating on germanium, with alternating high and low index layers is expected to give transmittance value greater than 93% in the studied wavelength region.

Subject Keywords

Physics.

URI

http://etd.lib.metu.edu.tr/upload/12611308/index.pdf
https://hdl.handle.net/11511/19220

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

B. Üçer, “Design and production of antireflection coating for Ge, ZnSe and ZnS in 8-12 micrometer wavelength region,” M.S. - Master of Science, Middle East Technical University, 2009.