A type of visible-absorbing, infra-red transmitting filter is described in which the absorbing units are produced from a plastic film that also serves as a supporting medium. Filters of this kind prepared from polyvinyl chloride and polyvinylidene chloride films are characterized by transmission bands between 1 and 3.3µ and between 3.5 and 5.8µ. Ways of isolating either of these bands are described. Such filters have obvious utility in connection with photoconductive cells.
ELKAN R. BLOUT, RICHARD S. CORLEY, and PATRICIA L. SNOW, "Infra-Red Transmitting Filters. II. The Region 1 to 6µ," J. Opt. Soc. Am. 40, 415-418 (1950)