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).

该项目的主要目标是提供激光引起的超快结构变化及其通过超短 X 射线脉冲的时间分辨分析的理论描述，特别是，我们建议执行： - 超快相变（固-液）的模拟。 - 计算激光诱导超快结构变化期间的时间演化、时间依赖性 X 射线衍射特性以及时间依赖性 X 射线吸收精细结构最近，我们的小组开发了一种理论方法，可以模拟任意形状的飞秒激光脉冲在固体中引起的非平衡、超快相变和烧蚀，该方法已被证明可以正确描述激光引起的金刚石结构变化。我们的方法包括原子运动的分子动力学模拟，其基于时间相关的势能表面，后者是从微观电子哈密顿量获得的，并且还明确包括激光激发。我们的目标首先是将这种方法扩展到处理其他材料（Si、Ge 和 InSb），并将超快结构变化的分子动力学模拟与可使用超短波测量的时间相关可观测量的计算相结合。我们计划使用动态衍射理论和现代 X 射线吸收精细结构理论 (EXAFS) 来计算激光诱导相变和结构变化期间摇摆曲线和 EXAFS 光谱的变化。将与 von der Linde/Sokolowski-Tinten（埃森大学）、Sauerbrey（耶拿大学）和 Falcone（加州大学伯克利分校）实验小组长期合作制定。