Superfluorescence and amplified spontaneous emission of 29-cm-1 phonons in ruby.

Abstract

Superfluorescence and amplified spontaneous emission of 29-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ phonons are observed following inversion of the E\ifmmode\bar\else\textasciimacron\fi{}${(}^{2}$E)-2A\ifmmode\bar\else\textasciimacron\fi{}${(}^{2}$E) acoustic transition of ${\mathrm{Cr}}^{3+}$ in ruby. The conditions for both of these manifestations of phonon avalanches are selected via the ${\mathrm{Cr}}^{3+}$ concentration. Superfluorescence is described in terms of a pendulum equation of the acoustic Bloch vector. Rate equations of the level and phonon populations account for amplified spontaneous emission.