Optical glasses were produced using arsenic trisulfide as a network former and different sulfides as network modifiers. These glasses transmit infrared up to 12–13 microns in thicknesses useful for optical purposes. The transmission of glassy selenium was determined up to 21 microns and a few composite selenium glasses were investigated.
RUDOLF FRERICHS, "New Optical Glasses with Good Transparency in the Infrared," J. Opt. Soc. Am. 43, 1153-1157 (1953)