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11 September 1989 Infrared Rugate Filters By Laser Flash Evaporation Of ZnS and ZnSe
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Rugate filters have come under considerable investigation over the last several years. Their attraction stems from two possibilities, 1) the creation of almost any kind of filter and 2) the graded index nature of these films should make them more robust. The index - thickness profiles necessary to make these filters can be quite complex. The rather sophisticated feedback control system required to fabricate these films has made progress difficult. Most rugate filters have been designed and fabricated for use in the visible and near infrared portion of the spectrum. Filters designed for regions beyond 1.4μ become very thick, where stress in the films becomes severe and the films delaminate. We report here the fabrication of rugate filters at wavelengths from 1.0 μ to 11μ. By varying the refractive index with film thickness, a reflection or transmission band may result at a specific wavelength. With a well chosen index versus film thickness profile, the filter can be tailored to cause narrow band reflection spikes at any wavelength and yet allow transmission of broadband radiation. The principle of the rugate filter is similar to the principle of multilayer dielectric stack filters such as the quarter-wave stack. Major differences exist, however, in the way they are physically realized. In the rugate filter, the discontinuous material interfaces of dielectric stacks are replaced by a controlled, gradually changing refractive index profile in the film. This index profile is achieved by changing the stoichiometry of a material (re.g., ZnSxSey ) as the film is deposited.
© (1989) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
C. S. Bartholomew, M. D. Morrow, and N. P. Murarka "Infrared Rugate Filters By Laser Flash Evaporation Of ZnS and ZnSe", Proc. SPIE 1112, Window and Dome Technologies and Materials, (11 September 1989);

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