Optical constants of ZnSe in the far infrared

The absorption coefficient {α} and refractive index n of bulk polycrystalline ZnSe have been derived from transmission measurements over wave-number ranges of 30--200 cm^-1 and 250--600 cm^-1. Infrared multiphonon structures have been found and assigned. Variations of {α} and n are satisfactorily described by a single-harmonic-oscillator model for the dielectric constant. Variations in {α} caused by multiphonon processes suggest that anharmonic lattice dynamics are important above 250 cm^-1, especially for three-phonon processes, which include the fundamental TO({Γ}) mode.