23 January 2003 Observation and characterization of the Stierwalt effect in dielectric filters with model coating defects
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Many applications of infrared technology require the use of narrow bandpass filters with excellent out-of-band rejection. Frequently, system designs require that the filter be placed in close proximity to a detector or focal plane array. More than twenty-five years ago Donald Stierwalt discovered that some filters that met out-of-band rejection specifications in a spectrophotometer did not meet specification when integrated into a focal plane assembly. In fact, he reported that proximal to the detector, one filter passed three orders of magnitude more out-of-band light. Since then, the Stierwalt Effect has become widely quoted and poorly studied. Many assume that it has to do with scatter in the film, but very little data has been reported. Here, we report the observation of the Stierwalt effect in an optical filter that was seeded with model defects. The seeding was done by depositing sparse 1μm polystyrene spheres upon a clean substrate before sputter depositing a simple band-stop filter. Light rejection from filters prepared in this way showed a strong dependence upon the distance between the film and the detector. Filters deposited without the spheres showed a much smaller effect.
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Peter D. Fuqua, Peter D. Fuqua, James D. Barrie, James D. Barrie, Nathan Presser, Nathan Presser, } "Observation and characterization of the Stierwalt effect in dielectric filters with model coating defects", Proc. SPIE 4820, Infrared Technology and Applications XXVIII, (23 January 2003); doi: 10.1117/12.453579; https://doi.org/10.1117/12.453579

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