Experimental test of the modified optical Bloch equations for solids using rotary echoes

Measurements of optical rotary-echo decay of the $R_1$(-1/2),σ transition of ${\mathrm{Cr}}^{3+}$ in dilute ruby at 2 K are described and compared with predictions of two recent modifications (Gauss-Markov and random-telegraph models) of the optical Bloch equations (OBE’s). While the modified OBE approximately describes the free-induction decay behavior both in ${\mathrm{Pr}}^{3+}$:${\mathrm{LaF}}_3$ and ruby, we show that rotary-echo decay in ruby is instead described by the standard OBE. Various aspects of the spin flip-flop model used in the theories are discussed in regard to ruby, as well as other possible dephasing contributions.