Doubly resonant Raman electron paramagnetic transitions ofCr3+in ruby(Al2O3:Cr3+)

Abstract

We report the Raman electron paramagnetic resonance (EPR) of ${\text{Cr}}^{3+}$ in ruby $({\text{Al}}_{2}{\text{O}}_{3}:{\text{Cr}}^{3+})$ in the ${^{4}A}_{2}$ (ground) and $\overline{E}$ (excited) states of its well-known ${R}_{1}$ emission line. Using tunable dye laser excitation within the range of the Zeeman components of ${R}_{1}$, we observe highly selective doubly resonant enhancements of the Raman EPR lines. The double resonances confirm the assignments of the Raman EPR lines, and they underscore the simultaneous occurrence of both ``in resonance'' and ``out resonance'' as visualized in the Kramers-Heisenberg quantum-mechanical picture of inelastic light scattering. The $g$ factors of the ${^{4}A}_{2}$ and $\overline{E}$ states are consistent with the observed magnetic field dependence of the Raman EPR shifts. Through the interplay of Raman effect and the sharp Zeeman components of ${R}_{1}$, the results provide clear insights into the underlying microscopic mechanism of these resonant Raman EPR spectra of ruby.