Time-Domain Light Scattering Spectroscopy of Condensed Matter

提出了一种利用新的时间分辨光谱技术研究凝聚态动力学中几个相关问题的综合实验方案。“脉冲”受激拉曼、布里渊和瑞利散射技术将在飞秒到纳秒的时间尺度上进行，以检查晶体在结构相变、无公度晶相、以及粘弹性和“简单”的流体。在这些系统中重要的强耦合、高耗散模式将通过直接观察它们的依赖于时间的运动来表征。在结构相变附近的晶体中，将研究无公度相中的序参数和声学模式(通常被过度抑制)。在液体-玻璃化转变区域附近的粘弹性流体中的色散声学行为将被描述。最后，我们将阐明简单分子液体中取向运动的衰减振动(即惯性)性质。所用的时间域方法是对这些系统的传统频域光散射谱的补充，因为它非常适合于表征这些类型的甚低频模式、严重衰减(包括过阻尼)模式、色散模式和强耦合模式。要研究的物质类别在行为上的相似性将有助于实验工作和分析，以及对结果的理论解释。

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.