Excitation-induced frequency shift probed by stimulated photon echoes

A stimulated photon-echo study has verified the instantaneous shift (≤1 MHz) and subsequent restoration (∼2 ms) of the transition frequency of an impurity ion in a solid when its neighboring ions are exposed to pulsed optical excitation. Experiments were conducted by monitoring the echo intensity for the ${}_{}{}^7{}_{}{}^{}$ ${\mathit{F}}_{0\mathrm{-}}^5$ ${\mathit{D}}_0$ transition of Eu ions in one site of ${\mathrm{Y}}_2$ ${\mathrm{SiO}}_5$, while exciting the other site. A photon-echo theory taking account of the stochastic frequency recovery is developed to explain the observations.