Persistent nonphotochemical spectral hole dynamics for an infrared vibrational mode in alkali halide crystals

The dynamics of persistent nonphotochemical spectral-hole production in the ${\nu }_3$ vibrational mode absorption of Re${\mathrm{O}}_4^{-}$ molecules in alkali halide crystals are described and analyzed. The holes form at low temperatures with laser powers orders of magnitude below the saturation intensity $I_s$. The holes are shallow with steady-state widths and depths that are independent of burning laser power. As a function of burning time, the holes grow very slowly, with a near-logarithmic growth at short burning times and a less-than-logarithmic growth at long times. The holes may be erased using laser irradiation at frequencies near the hole frequency. A model is presented for this process in which reorientational tunneling between librational levels occurs during nonradiative vibrational decay. This photon-induced molecular reorientation model accounts for most of the observed properties. The observation of persistent spectral holes for a high-symmetry photostable molecule in an ordered, crystalline host shows that nonphotochemical hole burning is a general solid-state phenomenon that can be expected to occur whenever the complete ground state of a system has configurational degeneracy.