Frequency and temperature dependence of the TO phonon-polariton decay in GaP - art. no. 104304

The temperature and frequency dependence of the decay time of the transvers e optical (TO) phonon polariton in GaP has been measured by impulsive stimu lated Raman scattering with 25-fs optical pulses. Tuning of the polariton f requency from 365 to 361 cm(-1) reveals drastic changes of the polariton de cay time with temperature. This result is explainable by third-order anharm onic decay of polaritons into two acoustic phonons taking into account the temperature-dependent shift of the van Hove singularity in the two-phonon d ensity of states of the acoustic phonons at the edge of the Brillouin zone. The frequency dependence of the TO phonon-polariton decay times measured a t different temperatures allows one to directly observe the shift of this s ingularity with temperature.