A simple filtering system, involving the use of only two simply constructed selenium powder filters, is described, by the use of which it is possible to obtain a pure energy spectrum with a wire grating spectrometer in the region 40–130µ. In addition transmission curves are given for a number of substances in the regions 1–15µ and 35–130µ.
R. BOWLING BARNES and LYMAN G. BONNER, "Filters for the Infrared," J. Opt. Soc. Am. 26, 428-433 (1936)