High-performance multilayer interference filters for the region 12-50μm

Abstract

The realization of filters containing PbTe and various II-VI materials to an optimum performance is described. In the pass-band, transmission is optimum due to the use of the Tschebysheff equal-ripple design concept; in the stopping bands, performance is optimum due to PbTe photoconductive absorption (low-pass) and II-VI reststrahl absorption (high-pass). Two example filters are discussed in detail: a cut-on/cut-off filter for the 668 cm^-1 v₂ band of CO₂ useful in space research and a long-wave blocking filter cutting on a 490 cm^-1 useful in infrared grating spectrophotometers.