A Frustrated Total Reflection Filter for the Infra-Red

Abstract

The Frustrated Total Reflection filter is a transmission band pass filter. It can be constructed for any part of the spectrum for which there exist transparent materials of different indices of refraction. Measurements are shown of a filter which was designed for the rocksalt infra-red region. This filter has two oppositely polarized pass bands which, at a particular angle of incidence, are at 4½ and 5 microns, respectively. Both the pass bands are approximately 1/10 of a micron wide. They can be shifted over a range of approximately half a micron by tilting the filter.