Time-Domain Light Scattering Spectroscopy of Condensed Matter

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A comprehensive experimental program for the study of several related problems in condensed-matter dynamics using novel time- resolved spectroscopy techniques is proposed. "Impulsive" stimulated Raman, Brillouin, and Rayleigh-scattering techniques, which taken together comprise an all-time-domain form of light-scattering spectroscopy, will be carried out on femtosecond through nanosecond time scales to examine the dynamics of crystals near structural phase transitions, incommensurate crystalline phases, and viscoelastic and "simple" fluids. Strongly coupled, highly dissipative modes important in these systems will be characterized through direct observation of their time-dependent motions. In crystals near structural phase transitions, the (often overdamped) order parameter and acoustic modes in incommensurate phases will be examined. Dispersive acoustic behavior in viscoelastic fluids near the liquid-glass transition region will be characterized. Finally, the damped vibrational (i.e. inertial) nature of orientational motion in simple molecular liquids will be elucidated. The time-domain approach used complements conventional frequency-domain light-scattering spectroscopy of these systems since it is well suited for characterization of very low-frequency modes, heavily damped (including overdamped) modes, dispersive modes, and strongly coupled modes of these types. The similarities in behavior of the classes of matter to be studied will facilitate experimental work and analysis as well as theoretical interpretation of results.