MRI: Development of a Femtosecond Time-Resolved Electron Diffraction System

这项来自重大研究仪器计划的奖项支持老道明研究基金会飞秒电子衍射系统的开发。时间域动力学检测需要一个与扰动系统的弛豫过程相当或更短的时间分辨率的探测器，对于许多固态和分子反应来说，扰动系统的驰豫过程在几个皮秒或飞秒范围内。基于电子和X射线衍射的超快时间分辨结构探针的开发引起了人们的极大兴趣。时间分辨电子衍射已被用来研究表面和薄膜中的相变，并探索激光激发分子的核动力学。由于仪器开发的需要，它的使用仅限于少数几个群体。优化的时间分辨电子衍射系统的工作电压为20-50keV，时间分辨率为100fs，每个脉冲的电子数为103-104。这将提供比目前的时间分辨电子衍射系统至少高几倍的时间分辨率和电子密度。该设计将最大限度地减少由于光电子能量扩散和空间电荷效应造成的电子轨迹差异。还提出了一种特殊的电子色散补偿元件。研究生将参与飞秒电子衍射系统的设计、建造和使用，以探测表面和薄膜反应。这些学生将获得超快激光、电子光学、泵浦探测技术和材料表征方面的经验。本科生将作为技术助理和高级设计项目的一部分参加。这一奖项来自主要研究仪器计划，以支持在Old Dominion研究基金会开发高速电子衍射系统。固体和分子中的许多重要反应发生在皮秒或更短的时间尺度内，因此，需要开发能够高速探测的仪器。当电子从固体或分子射流中衍射时，产生的衍射图提供了关于固体或分子结构的信息。使用超短激光脉冲引发反应，并使用与激光脉冲延迟的同等超短电子脉冲作为探针，可以对反应进行时间解析。由于复杂仪器发展的需要，高速电子衍射仪的使用已被限制在少数几组。将开发一种优化的高速电子衍射系统。这将提供比目前的时间分辨系统至少高几倍的时间分辨率，使人们能够观察到许多目前尚未很好理解的现象。提出了一种最小化电子脉冲展宽并引入特殊的电子色散补偿元件来压缩电子脉冲的新设计。研究生将参与飞秒电子衍射系统的设计、建造和使用，以探测科学和技术感兴趣的表面和薄膜反应。这些学生将获得激光、电子光学和材料表征方面的经验。本科生将作为技术助理和高级设计项目的一部分参与。这一经历将为他们在工业、政府和学术背景下的高科技职业生涯做好准备。

This award from the Major Research Instrumentation Program supports the development of a femtosecond electron diffraction system development at Old Dominion Research Foundation. Time domain dynamical examination requires a probe with comparable or shorter temporal resolution than the relaxation process of the perturbed system, which for many solid-state and molecular reactions is in the few picosecond or femtosecond range. There is a significant interest in developing ultrafast time-resolved structural probes based on electron and x-ray diffraction. Time-resolved electron diffraction has been used to study phase transitions at surfaces and in thin films, and to probe the nuclear dynamics of laser excited molecules. Because of the need for instrumentation development, its use has been limited to few groups. An optimized time-resolved electron diffraction system operating at 20-50 keV with 100 fs temporal resolution and 103-104 electrons per pulse will be developed. This will provide at least several times higher temporal resolution and electron density than present time-resolved electron diffraction systems. The design will minimize electron trajectory differences due to photoelectron energy spread and space charge effects. The introduction of a special electron dispersion compensation element is also proposed. Graduate students will be involved in design, construction, and use of the femtosecond electron diffraction system to probe surface and thin film reactions. These students will gain experience in ultrafast lasers, electron optics, pump-probe techniques, and material characterization. Undergraduate students will participate as technical assistants and as part of their senior design projects.This award from the Major Research Instrumentation Program supports the development a high-speed electron diffraction system at Old Dominion Research Foundation. Many important reactions in solids and molecules occur in a time scale of a picosecond or shorter, therefore, there is a need to develop instrumentation capable of high-speed probing. When electrons are diffracted from a solid or a molecular jet, the produced diffraction pattern provides information on the solid or molecular structure. Using an ultrashort laser pulse to initiate a reaction and an equally ultrashort electron pulse, delayed from the laser pulse, as a probe, it is possible to time resolve the reaction. Because of the need for complex instrumentation development, the use of high-speed electron diffraction has been limited to few groups. An optimized high-speed electron diffraction system will be developed. This will provide at least several times higher temporal resolution than present time-resolved systems, enabling the observation of many phenomena not presently well understood. A new design minimizing electron pulse spread and introducing special electron dispersion compensation element for electron pulse compression will be developed. Graduate students will be involved in design, construction, and use of the femtosecond electron diffraction system to probe surface and thin film reactions of scientific and technological interest. These students will gain experience in lasers, electron optics, and material characterization. Undergraduate students will participate as technical assistants and as part of their senior design projects. This experience will prepare them for a career in high technology within an industrial, governmental and academic setting.