Multiple-Pulse, Single-Shot Femtosecond Spectroscopy of Condensed Phases

在化学系物理化学计划的这个项目中，麻省理工学院的Keith A.Nelson教授将在分子和材料行为的光学控制领域进行一系列持续的研究，包括凝聚介质中的结构和化学重排。这些研究依赖于在可见光、近红外或近紫外线波长使用多脉冲飞秒光谱。成形的飞秒脉冲序列将被用来驱动晶格中的大幅度振动，以便能够对远离平衡的晶体几何进行光谱观察。其他工作将集中在开发自动时域振动光谱仪、操纵电子相干以观察只有通过双光子跃迁才能进入的电子水平上的相干波包动态，以及其他专题。研究的初始阶段将致力于实施产生、表征和放大复杂飞秒波形的改进方法。目前物理化学的前沿研究包括在超短时间尺度上研究分子过程，这些时间尺度对应于一个分子振动的周期(几飞秒)。这些研究有可能为控制分子反应和其他动力学过程提供方法，以及提供核磁共振技术的光学模拟来研究凝聚相光学光谱。

In this project in the Physical Chemistry Program of the Chemistry Division, Prof. Keith A. Nelson of the Massachusetts Institute of Technology will engage in a series of continuing investigations in the field of optical control of molecular and material behavior, including structural and chemical rearrangements in condensed media. These studies rely on the use of multiple-pulse femtosecond spectroscopy at visible, near-infrared or near-ultraviolet wavelengths. Shaped femtosecond pulse sequences are to be used to drive large-amplitude vibrations in crystal lattices to enable the spectroscopic observation of far-from-equilibrium crystal geometries. Additional work will concentrate on the development of an automated time-domain vibrational spectrometer, the manipulation of electronic coherences to observe coherent wavepacket dynamics in electronic levels accessible only through two-photon transitions, and other topics. The initial stages of the research will be devoted to the implementation of improved methods for the generation, characterization, and amplification of complex femtosecond waveforms. Current forefront research in physical chemistry includes the study of molecular processes at ultra-short time scales that correspond to the period of one molecular vibration ( a few femtoseconds). These investigations have the potential of providing methods for the control of molecular reactions and other dynamical processes, as well as providing optical analogs of the nuclear magnetic resonance technique to study condensed phase optical spectroscopy.