Role of pure dephasing in the broadening of zero-phonon emission lines in ruby

A theoretical analysis is made of the homogeneous linewidth of the electronic Raman transition between ē and 2ā excited states of Cr³⁺ observed in optically pumped ruby, in comparison with the widths of the phosphorescence R₁ and R₂ lines. In particular, we consider the phenomenological correlation between the broadening processes of the ē and 2ā levels, implied by the experimental fact that the magnitude of the Raman linewidth is approximately equal to the average, rather than the sum, of the R₁ and R₂ linewidths. The origin of this correlation is shown to be the quenching of pure-dephasing processes, associated with elastic phonon scattering, of the ē ? 2ā transition, while the pure-dephasing rates of the phosphorescence transitions are comparable to the rates of population-relaxation (lifetime-broadening) processes, associated with inelastic phonon scattering.