VIBRATIONAL DYNAMICS IN CONDENSED MATTER PROBED WITH LINAC BASED FELS

The super-conducting linac pumped free electron laser (FEL) at Stanfor d has been used to study the vibrational dynamics of molecules in liqu ids and glasses. A variety of experiments have been performed, includi ng the world's first vibrational photon echo experiments in liquids an d glasses and polarization selective pump-probe experiments. In this p aper vibrational photon echo experiments are described and characteris tics of the FEL important to these experiments are discuss. Vibrationa l. photon echo experiments were performed on the asymmetric CO stretch ing mode of tungsten hexacarbonyl (1976 cm(-1)) in the organic glass d ibutylphthalate as a function of temperature using sub-picosecond infr ared pulses. The echo decays display pronounced beats and are bi-expon ential. The beats and bi-exponential decays arise because the bandwidt h of the transform limited FEL pulses exceeds the vibrational anharmon icity, leading to the excitation and dephasing of a multilevel coheren ce. From the beat frequency, the anharmonicity is determined to be 14. 7 cm(-1). From the bi-exponential decay components, the temperature-de pendent homogeneous vibrational dephasing rates of both the v = 0 --> 1 and v = 1 --> 2 transitions are determined.