Multiphonon infrared absorption in highly transparent MgF2

Abstract

We report the first detailed polarized-absorption measurements for Mg${\mathrm{F}}_2$ in the 5-10-μm regime, at both room and liquid-nitrogen temperatures. The observed spectra are attributed to intrinsic multiphonon absorption, and differences in the polarized spectra are interpreted as indicating the persistence of selection rules into the three-phonon regime.