Observation of hole burning and cross relaxation effects in ruby

In this paper we report, for the first time, the observation of optical hole burning in a solid, ruby. In addition, we describe experimental results which show that optical saturation of the inhomogeneously broadened R₁ line in ruby at 4.2^∘{}K occurs not only for ions in resonance with the saturating radiation but also for ions at frequencies up to about 50 MHz away from the radiation frequency. This result and others are consistent with a model in which cross relaxation occurs in the ground-state levels between ions in resonance with the laser beam and nonresonant ions.