25 August 2010 Investigation of the temperature dependent complex index of refraction of infrared thin-film coating materials
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The use of IR optical substrates and thin-films is an integral part of optical system construction for remote sensing instrumentation. From telescopes to multi-spectral imagers, entire optical systems can be built with a relatively small set of materials. The temperature dependence of the optical, mechanical and electronic properties of bulk infrared (IR) materials has been well characterized in the literature [1-5]. Manufacturer and research reports provide some representation of the impact of temperature excursions on the index of refraction (dn/dT), and the absorption profile (dk/dT) of bulk crystalline germanium (Ge) and synthetic crystalline zinc sulphide (ZnS). The availability of empirical data for thin-films, however, is much more limited. These optical constants for as-deposited amorphous thin-films of Ge and ZnS are investigated. Models for the temperature dependent refractive index have been developed using transmittance and reflectance data over the wavelength region between 2.0-20.0 μm. The spectra of manufactured filters are characterized at ambient and cryogenic temperatures (300K-50K) in order to validate the models developed.
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Lucas C. Alves, Lucas C. Alves, "Investigation of the temperature dependent complex index of refraction of infrared thin-film coating materials", Proc. SPIE 7786, Current Developments in Lens Design and Optical Engineering XI; and Advances in Thin Film Coatings VI, 778619 (25 August 2010); doi: 10.1117/12.868479; https://doi.org/10.1117/12.868479

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