Coherent lattice vibrations in lithium tantalate have been observed directly in the time domain by use of femtosecond optical pulses and the electro-optic effect to coherently excite and detect phonon polaritons. The damping time of the lowest transverse optic phonon has been determined directly from the decay rate of these oscillations. This measurement establishes an intrinsic speed limit for the electro-optic response of this material.

• Received 22 August 1985

DOI:https://doi.org/10.1103/PhysRevLett.55.2152