Trapping of point-contact-generated 29-cm-1 phonons in ruby.

Abstract

Trapping of 29-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ phonons by optically excited ${\mathrm{Cr}}^{3+}$ ions in ruby is studied at phonon occupations of up to order unity. The 29-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ phonons are supplied by transient excitation of a metallic point contact and subsequent conversion of the injected phonons to resonance. The growth and the decay of the trapped phonon population are markedly non-single-exponential quantities, particularly at higher phonon populations. A quantitative analysis of these effects is made on the basis of phenomenological rate equations of the ion and phonon populations. These equations make explicit allowance for the line shape of the E\ifmmode\bar\else\textasciimacron\fi{}${(}^{2}$E)-2A\ifmmode\bar\else\textasciimacron\fi{}${(}^{2}$E) phonon transition as well as for feeding and loss of resonant phonons by mediation of weakly exchange-coupled ${\mathrm{Cr}}^{3+}$ pairs. At the higher phonon occupations, the transition appears to be dynamically broadened by stimulated phonon emission, which reduces the trapping efficiency.