International Research Fellowship Program: Laser-Based Femtosecond X-Ray Development and Application

国际研究奖学金计划使美国科学家和工程师能够在国外进行三到二十四个月的研究。该计划的奖项提供了联合研究的机会，以及使用独特或互补的设施，专业知识和国外的实验条件。在法国帕莱索的光学显微镜实验室，Shah与Antoine Dinse博士一起工作。在100多年的时间里，X射线已经成为科学家们窥视原子尺度结构的最有力的工具之一。在各种技术中，X射线光谱学消除了对晶体的需要，这一要求严重限制了这种原子可视化的研究范围。这项工作推动了X射线科学在数百飞秒的时间尺度上对分子进行动态研究，方法是：（1）从超强激光脉冲中开发出超快、定向和宽带X射线源;（2）利用它通过X射线光谱法识别化学反应中的飞秒重排。该主机站点是激光研究人员开发100太瓦，10 Hz激光器的地方，这项工作将与Antoine Drachse和飞秒X射线物理组合作完成，他们是超快X射线源开发和衍射研究领域的先驱。该研究更具体地研究了使用晶体光谱仪的源光谱，这与电子束特性以及等离子体密度相关，由注入氦气的密度控制。化学、生物学和固态物理学都是依赖于X射线来识别分子结构的学科。光学研究表明，这些学科中的每一个系统都以飞秒的时间尺度发展，但没有提供X射线的结构细节。因此，这种明亮的超快x射线源，是大学实验室规模的，具有深远的影响。该源用于定量X射线吸收光谱的实用性的证明将引入一种有价值的新工具，具有衍射技术的独特优势，用于超快X射线研究。

0502281ShahThe International Research Fellowship Program enables U.S. scientists and engineers to conduct three to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-two-month research fellowship by Dr. Rahul C. Shah to work with Dr. Antoine Rousse at the Laboratoire Optique Appliquee in Palaiseau, France.In a little over 100 years, x-rays have become one of the most powerful tools scientists have for peering into atomic scale structures. Among the various techniques, x-ray spectroscopy obviates the need for crystals, a requirement which severely limits range of studies for such atomic visualization. This work pushes x-ray science into dynamical studies of molecules at timescales of hundreds of femtoseconds by (1) developing an ultra-fast, directional, and broadband x-ray source from ultra-intense laser pulses and (2) utilizing it to identify femtosecond rearrangements in a chemical reaction by x-ray spectroscopy. The host site is where laser researchers have developed a 100 Terawatt, 10 Hz laser, and the work will be done in collaboration with Antoine Rousse and the Femtosecond X-ray Physics group, pioneers in the field of ultrafast x-ray source development and diffraction studies. The research more specifically studies the source spectrum by use of crystal spectrometer, and this is correlated with electron beam characteristics as well as plasma density, controlled by the density of the injected helium gas. Chemistry, biology, and solid state physics are all disciplines which have relied on x-rays for identification of molecular structures. Optical studies have indicated that systems in each of these disciplines evolve at femtosecond timescales but do not provide the structural details of x-rays. Thus this bright source of ultrafast x-rays which is of university laboratory scale stands to have far reaching impact. Demonstration of the usefulness of the source for quantitative x-ray absorption spectroscopy will introduce a valuable new tool, with advantages unique from diffraction techniques, to ultrafast x-ray studies.