Coherent optical phonons in pure and Pr3+ doped YAG crystal studied by Optical Kerr Effect spectroscopy: Temperature and concentration dependence

- Time evolution of coherent phonons in Pr:YAG was observed.
- Temperature dependence of phonon lifetimes and frequencies was measured.
- A 3-phonon relaxation process fits the observed temperature dependence.
- Anharmonic coupling constants and Raman linewidths were calculated.
- Dopant concentration dependence of phonon modes was investigated.

Herewith we present the results of the investigation of coherent phonons in pure and Pr3+ doped YAG crystals, by means of the femtosecond Optical Kerr Effect spectroscopy. In the experiment we have followed the dynamics of the Raman-active phonon modes at different temperatures in range between 263 K and 373 K and for different dopant concentrations. We found that the temperature dependence of phonon frequencies and lifetimes is linear, which is characteristic for 3-phonon relaxation process. We have used our fit results to calculate the widths of homogeneously broadened Raman lines and to find the anharmonic coupling constants. The observed dependence of phonon frequency and lifetime on dopant concentration is interpreted in terms of small, dopant induced alterations in the crystal structure, where the most influenced modes involve motion of the substituted ion. High precision of the OKE experiment is of great value, as such changes are small and thus hard to measure, when only low doping is possible, which is the case for Pr:YAG.

127