Two-phonon combination states driven by second order Raman scattering in KTaO/sub 3/

Summary form only given. The investigation of coherent phonons has been a field of extensive efforts since the first observation of coherent phonons in 1990. Several excitation mechanisms for coherent phonons in solids have been identified among which the most prominent is impulsive stimulated first order Raman scattering. Coherent states exhibit an oscillating expectation value of the phonon amplitude of a given mode while the statistic properties like amplitude variances and covariances remain static. However, dynamics of these statistic variables can be driven by second-order Raman-scattering (SOR), e.g., oscillating amplitude variances (phonon squeezed states) as first reported by Garret et al. Here we report-to our knowledge for the first time-on correlated states of phonon-mode-pairs consisting of different phonons driven by ultrashort light pulses. KTaO/sub 3/, is the ideal material for this study since first order Raman processes are not allowed.