New High-Energy Monoenergetic Source for Nanosecond Phonon Spectroscopy

A new monoenergetic nanosecond pulsed source of high-energy phonons is described for doing time-resolved phonon spectroscopy. The phonons, internally generated by excited-state spin-lattice relaxation following optical excitation with a pulsed tunable dye laser, are monitored with nanosecond resolution from enhanced emission of the upper excited state due to resonant absorption. The technique is applied to the determination of the inelastic scattering time of 29-${\mathrm{cm}}^{-1\mathrm{}}$ phonons in ruby (${\tau }_p=530\mathrm{}$ ns).