Time-resolved Spectroscopy of Anharmonic Systems

马萨诸塞州理工学院的基思纳尔逊得到了 实验物理化学计划在他的继续 大振幅晶格振动的时间和 空间分辨飞秒光脉冲整形技术。 起初， 他将专注于经历结构相变的晶体， 特别是不同铁电相之间的切换。 在 此外，他将着眼于半导体材料，其带隙可能是 受光诱导大振幅 相干晶格振动 纳尔逊还计划检查这种行为 光脉冲在分子晶体中引起沿着运动 反应坐标影响结晶化学反应。 他将 研究块状和薄膜钙钛矿以研究结构相 跃迁和声子极化激元腔;二乙炔， 芘用于研究分子晶体; Ti 2 O3和GeTe用作半导体。 纳尔逊教授已经证明，显著的核位移可以 在分子晶体中使用高能脉冲诱导。 此外，本发明还提供了一种方法， 如果波长足够长，则对晶体的损害最小化。 在 这些研究纳尔逊将调查替代策略， 实现大的核位移和什么类型的影响， 分子特性对最优策略的影响。 纳尔逊教授将应用他的实验室开发的技术， 将飞秒光脉冲用于各种材料， 铁电晶体和小间隙半导体，以便 确定是否有可能影响化学变化。 除了 这项工作可能会给晶格领域带来的直接进步 光谱学和分子过程的光学控制，它可以 预计计划中的研究将具有技术意义 和实用性的设计师的原型设备的光开关， 信息传输。

Keith Nelson of the Massachusetts Institute of Technology is supported by the Experimental Physical Chemistry Program in his continuing investigations of large amplitude lattice vibrations using time- and space-resolved femtosecond optical pulse-shaping techniques. Initially, he will focus on crystals that undergo structural phase transitions, in particular the switching among different ferroelectric phases. In addition, he will look at semiconducting materials whose bandgaps may be influenced and perhaps closed by optically induced large-amplitude coherent lattice vibrations. Nelson also plans to examine the behavior of molecular crystals in which the optical pulses induce motion along reaction coordinates to affect crystalline chemical reactions. He will investigate both bulk and thin film perovskites to study structural phase transitions and phonon-polariton cavities; diacetylene, perylene and pyrene to study molecular crystals; and Ti2O3 and GeTe as semiconductors. Prof. Nelson has demonstrated that significant nuclear displacements can be induced in molecular crystals using high energy pulses. In addition, if the wavelength is long enough, damage to the crystal is minimized. In these studies Nelson will investigate alternative strategies for achieving large nuclear displacements and what types of effects the molecular properties have on the optimum strategy. Prof. Nelson will apply techniques developed in his laboratory that exploit femtosecond optical pulses to a wide variety of materials such as ferroelectric crystals and small gap semiconductors, in order to determine if it is possible to effect a chemical change. In addition to the direct advances this work will likely offer to the fields of lattice spectroscopy and optical control of molecular processes, it can be anticipated that the planned research will be of technological interest and utility to designers of prototype devices for optical switching and information transmittal.