Time-dependent diffraction and EXAFS during laser induced ultrashort structural changes: theory and simulations

激光诱导超短结构变化期间的时间相关衍射和 EXAFS：理论和模拟

• 批准号: 5373036
• 负责人: Professor Dr. Martin Ezequiel Garcia
• 金额: --
• 依托单位: Institut für Theoretische Physik
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2002
• 资助国家: 德国
• 起止时间: 2001-12-31 至 2009-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/5373036?language=en
• 关键词: Time; dependent; diffraction; EXAFS; during

The main goal of this project is to provide a theoretical description of laser induced ultrafast structural changes and of their time-resolved analysis through ultrashort x-ray pulses. In particular, we propose to perform: - Simulations of ultrafast phase transitions (solid-liquid and solid-solid) in Silicon, Germanium and InSb. - Calculation of the time evolution, during laser induced ultrafast structural changes, of time-dependent x-ray diffraction properties, and time-dependent x-ray absorption fine structure (EXAFS) spectra. Recently, our group has developed a theoretical approach which permits to simulate nonequilibrium, ultrafast phase transitions and ablation induced in solids by femtosecond laser pulses of arbitrary shape. The method has been shown to describe correctly laser induced structural changes in diamond, graphite and fullerenes. Our approach consist in molecular dynamics simulations for the atomic motion, which are based on time dependent potential energy surfaces. The latter are obtained from a microscopic electronic Hamiltonian and also include explicitly the laser excitation and thermalization effects. Our goal is first to extend this method to treat other materials (Si, Ge and InSb), and to combine the molecular dynamics simulations of the ultrafast structural changes with the calculation of time dependent observable quantities which can be measured using ultrashort x-ray pulses. We plan to use dynamical diffraction theory and modern theory of x-ray absorption fine structure (EXAFS) to calculate the changes of rocking curves and EXAFS-spectra during laser induced phase transitions and structural changes. Our theoretical project will be worked out in permanent collaboration with the experimental groups von der Linde/Sokolowski-Tinten (Universität Essen), Sauerbrey (Universität Jena) and Falcone (University of California, Berkeley).

该项目的主要目的是提供对激光诱导的超快结构变化及其通过超短X射线脉冲分析的理论描述。特别是，我们建议执行： - 硅，锗和Insb中超快相变（固液和固体）的模拟。 - 在激光诱导的超快结构变化，时间依赖性X射线衍射特性以及时间依赖性X射线抽象细胞（EXAFS）光谱期间的时间演化计算。最近，我们的小组开发了一种理论方法，该方法允许模拟非平衡，超快相变和消融，并通过飞秒激光脉冲在固体中诱导的固体脉冲。该方法已被证明可以正确描述激光诱导的钻石，石墨和富勒烯的结构变化。我们的方法包括基于时间依赖势能表面的原子运动的分子动力学模拟。后者是从微观电子哈密顿量获得的，还明确包括激光兴奋和热效应。我们的目标是首先扩展这种方法以处理其他材料（SI，GE和INSB），并将超快结构变化的分子动力学模拟与计算时间相关的可观察量的计算，可以使用超舒服的X射线脉冲来测量。我们计划使用动态衍射理论和X射线抽象精细结构（EXAFS）的现代理论来计算激光诱导的相变和结构变化期间摇摆曲线和EXAFS-Spectra的变化。我们的理论项目将与实验小组永久合作，von der Linde/Sokolowski-Tinten（UniversitätEssen），Sauerbrey（UniversitätJena）和Falcone（加利福尼亚大学，伯克利大学）。