Long-lived optical phonons in ZnO studied with impulsive stimulated Raman scattering

The anharmonic properties of the low-frequency ${E}_{2}$ phonon in ZnO were measured using impulsive stimulated Raman scattering. At 5 K, the frequency and lifetime are $(2.9789\ifmmode\pm\else\textpm\fi{}0.0002)\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$ and $(211\ifmmode\pm\else\textpm\fi{}7)\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$. The unusually long lifetime and the high accuracy in the determination of the frequency hold promise for applications in metrology, quantum computation and materials characterization. The temperature dependence of the lifetime is determined by two-phonon upconversion decay contributions, which vanish at zero temperature. Results suggest that the lifetime is limited by isotopic disorder and that values in the nanosecond range may be achievable in isotopically pure samples.