Determination of upper limits for spatial energy diffusion in ruby

Abstract

Direct measurements of the diffusion distance of $\overline{E}(^{2}E)$ state excitation by time-resolved degenerate four-wave mixing in ruby are reported. Measurements are made on crystals with ${\mathrm{Cr}}^{3+}$ concentrations varying between 0.05 and 1.55 at.% at 10\ifmmode^\circ\else\textdegree\fi{}K. In all cases an upper limit of 30 nm is determined for the diffusion distance within the fluorescence lifetime.