Multiphonon Absorption in NaF

The infrared absorption in NaF at the two CO₂ laser wavelengths 10.6 and 9.3 {μ}m was measured between 4 and 400 K. The results complement the previously measured absorption for higher temperatures, and allow for a detailed comparison with theoretical predictions. The experimental temperature dependence at 10.6 {μ}m can be excellently fitted by a curve expected for three-phonon processes in the whole temperature range; the absorption at 9.3 {μ}m fits a mixture of three- and four-phonon processes.