Optical dephasing by nonequilibrium phonons inLaF3

Phonon-induced coherence loss (PICL) is produced by a monoenergetic nonequilibrium distribution of phonons in ${\mathrm{LaF}}_3$:${\mathrm{Pr}}^{3+}$. The phonons are generated by relaxation between excited states of the ${\mathrm{Pr}}^{3+}$ ion after selective excitation with a pulsed, tunable dye laser. The optical dephasing is observed from the effect on the free-induction decay of ${\mathrm{Pr}}^{3+}$ ions whose excited-state level separation is resonant with the phonons. It is shown that PICL is a sensitive detector of monoenergetic phonons, and can be used to study phonon dynamics. The observed rate of optical dephasing is reduced relative to an equivalent occupation of 23-${\mathrm{cm}}^{\mathrm{-}1}$ phonons produced thermally.