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

The dynamics of persistent nonphotochemical spectral-hole production in the ν₃ vibrational mode absorption of ReO₄^- 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 Iₛ. 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.