Spectral Width of Optically Generated Bottlenecked 29-cm−1Phonons in Ruby

The ruby $R_2$-line intensity at 2.1 K is observed to be nearly quadratically depedent on the $R_1$ intensity, indicative of strongly bottlenecked 29-${\mathrm{cm}}^{-1\mathrm{}}$ phonons generated by the $2\overline{A}\left({}_{}{}^2{}_{}{}^{}E\right)\to \overline{E}\left({}_{}{}^2{}_{}{}^{}E\right)$ decay in the optical pumping cycle. The spectral width of the phonon excitation is probed by separating the degenerate phonon packets in a magnetic field and monitoring the decrease of the bottlenecking.