Ultrafast Imaging of Electronic Motion in Atoms and Molecules

: This project had both and experimental and theoretical component. In the experimental effort, a new setup was designed and constructed to deliver femtosecond electron pulses for scattering and diffraction experiments on a gaseous target of atoms or molecules. An optical setup was designed and constructed to compensate for the blurring of the temporal resolution due to the velocity mismatch between the laser and electrons, which we showed can be reduced to less than 100 fs. The charge and duration of the electron pulses were measured with a home-made faraday cup and laser-triggered streak camera, respectively. Both are retractable and can measure the beam in-situ. The gun was shown to generate pulses with more than a million electrons per pulse. The pulse duration was compressed from 20 ps to 700 fs, as measured with the streak camera. Active stabilization was implemented on the laser repetition rate and beam pointing to reduce the timing jitter. In the theory component of the project, we have calculated the distortion of a helium atom in an intense laser field in support of planned experimental measurements. We have developed a new theory for ultrafast electron diffraction from a time-varying coherent electronic state of a target atom or molecule that accounts for inelastic process.