This is a review of work devoted to the physical properties of optical
materials suitable for fabricating optical elements for lasers operat
ing in the 2-11-mu m range. Possible mechanisms for the breakdown of t
he elements are considered, and criteria are proposed for comparing ma
terials. The characteristics of various single-crystal and polycrystal
line materials are presented and compared. (C) 1996 The Optical Societ
y of America.