Subpicosecond time-resolved Raman investigation of optical phonon modes in Cr-doped forsterite

The nonradiative relaxation dynamics of forsterite was investigated by studying different phonon modes using time-resolved Raman spectroscopy. We found that only the 225, 335, and 370 cm^-1 anti-Stokes Raman lines exhibit changes in their intensity at various pump-probe delay times indicating the presence of nonequilibrium phonon populations. The experiments were performed at room and liquid nitrogen temperatures. A rate equations analysis was used to describe the dynamics of the ion-lattice system. The nonradiative relaxation time and the phonon lifetimes were estimated by fitting to the experimental data.