TIME-RESOLVED DIFFUSE SCATTERING FROM LASER-EXCITED SEMICONDUCTORS

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 强的超短激光脉冲为我们提供了一种通过激发相干声子来获得固体中非平衡态的方法。由于材料中的声子决定了材料的力学和热学性质，因此开发工具来研究激光诱导的非平衡声子布居的动力学是非常有意义的。此外，激光激发可以用来获得物质的其他非平衡相，例如，通过在高波矢处涉及晶格不稳定性的新型相变。 由于可见光辐射的波长很长，在光学实验中只访问了一小部分布里渊区。目前还没有实验技术可以提供固体完整声子分支的时间分辨信息。时间分辨X射线扩散散射(TRXDS)有可能成为研究晶体布里渊区这些非平衡过程的终极工具。我们建议用时间分辨的X射线漫反射来研究强激光辐照引起的硅和GaP的晶格不稳定性。拟议的实验是对APS时间分辨X射线扩散散射的可行性的测试，随着LCLS等新来源的出现，可能会使社区的大部分人受益。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Intense ultrashort laser pulses provide us with a way to access non-equilibrium states in solids by excitation of coherent phonons. Because the phonons in the material determine the mechanical and thermal properties it is of great interest to develop tools to study the dynamics of the nonequilibrium phonon population induced by the laser. In addition laser excitation can be used to access other nonequilibrium phases of matter through for example novel phase transitions involving lattice instabilities at high wavevector. Because of the long wavelength of visible radiation only a small volume of the Brillouin zone is accessed in optical experiments. There is currently no experimental technique that can provide time-resolved information of the complete phonon branches of the solid. Time-resolved x-ray diffuse scattering (TRXDS) has the potential to be the ultimate tool to study these nonequilibrium processes throughout the Brillouin-zone of the crystal. We propose to use time-resolved diffuse X-ray scattering to study the lattice instability of Si and GaP induced by intense laser irradiation. The proposed experiment serves as a test of the feasibility of time-resolved x-ray diffuse scattering at APS and could potentially benefit a large part of the community with the advent of novel sources as the LCLS.