Far infrared filters for the Galileo-Jupiter and other missions

Abstract

Extrapolation of PbTe/ii–vi multilayer interference-filter technique from 20 to beyond 40 μm is described and PbTe transparency reviewed; improvements below 20 μm are reported. A composite filter cutting on steeply at 40 μm is described that uses absorptive films of ZnS and As₂S₃, thin quartz, and supplementary multilayer interference. Absorptive filters are described containing the ii–vi compounds since these are found transparent at wavelengths shorter and longer than their reststrahl.