Persistent spectral hole burning for R’ color centers in LiF crystals: Statics, dynamics, and external-field effects

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Abstract
The persistent spectral hole-burning properties of R’ color centers in pure and doped LiF single crystals at liquid-helium temperatures are described and analyzed. Using frequency-modulation spectroscopy and precision ratiometric transmission spectroscopy, a satellite hole structure has been observed which varies with position in the inhomogeneous line due to excited-state splittings. Transient effects in the optical absorption indicate that an intermediate state with millisecond lifetimes is involved in hole formation. The persistent holes have been observed to grow as the logarithm of time and the logarithm of burning intensity in certain regimes, and a phenomenological tunneling model has been used to explain the time and intensity dependence. The results suggest that R’ centers interact via tunneling and local strains with a quasi-random distribution of nearby traps which may be other color centers in the host material. A linear Stark effect has been observed in agreement with earlier measurements. This work illustrates the power of hole-burning spectroscopy to uncover static and dynamic interactions normally hidden by inhomogeneous broadening.