Femtosecond Impulsive Stimulated Raman Scattering Studies of LiTaO₃

Impulsive stimulated Raman scattering (ISRS) experiments on LiTaO₃ were conducted over a wide range of scattering wavevectors. The results permit explanation of the anomalously high and wavevector-dependent damping rates of the low-frequency phonon-polariton mode in terms of coupling of the polariton to a weakly Raman-active low-frequency relaxational mode and to two heavily damped vibrational modes. ISRS experiments at low temperatures were made possible through the use of multiple-pulse ISRS experiments where photorefractive damage precluded experiments with single excitation pulses.