6 May 2009 High-performance MWIR dual bandpass filter for thermal imaging
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Abstract
Bandpass filters transmitting the 3.5 to 5.0μm atmospheric window while simultaneously blocking the 4.3μm CO2 absorption band are in demand. However, realization of these dual bandpass filters is challenging from the standpoint of coating design, material selection, and manufacturing process. JDSU's Ucp-1 magnetron sputtering platform is ideally suited to the production of these types of filters. It enables the use of coating materials with higher transmission and lower temperature shifts than conventional (i.e. thermally evaporated) MWIR materials. Ucp-1 also has excellent layer thickness control, which allows complex designs to be realized. The performance of a dual bandpass filter manufactured for AFRL as part of their "Exploration of Novel Band-pass Filter Designs" program is discussed. The filter achieved average transmission in the passbands of greater than 94% with filter slopes of 1.1% or less. Blocking of the CO2 band was less than 1%, and the below and above band blocking was less than 0.1%. All of the filter requirements were met over the temperature range of 77K to room ambient. We also discuss the results achieved in extending the above approach to the design and manufacture of a quadruple bandpass filter (with passbands centered at 1.23, 1.6, 2.2, and 3.75μm).
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Karen D. Hendrix, Adam Bergeron, David L. Favot, "High-performance MWIR dual bandpass filter for thermal imaging", Proc. SPIE 7298, Infrared Technology and Applications XXXV, 72982K (6 May 2009); doi: 10.1117/12.819944; https://doi.org/10.1117/12.819944
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