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

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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.