Laser saturation of the hydride ion local mode vibration in CaF2

We present a study of the localized vibrational mode of H- ions substituting F- ions in the calcium fluoride lattice. Using a tunable high pressure carbon dioxide laser we determined the linewidth and the saturation intensity of the H- local mode infra-red absorption line for temperatures between 10 K and 110 K. Our results indicate that energy relaxation of an excited H- vibrational mode occurs mainly by decay into three phonons with a lifetime for the localized mode of about 17 ps at low temperatures (T ≤ 10 K), which results in a Lorentzian line of width 0.33 cm-1. An analysis of our results shows that line broadening is caused mainly by energy relaxation at temperatures up to 60 K and by phonon Raman scattering at higher temperatures.