Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Design and Construction of a High-Current Femtosecond Gas-Phase Electron Diffraction Setup
We designed and constructed a state-of-the-art high current ultrafast gas electron diffraction experimental setup, which resolved two main challenges that constraint temporal resolution in previous setups. These aforementioned bottlenecks were: the space charge effect due to the Coulomb expansion, and the velocity mismatch between the sub-relativistic electrons (probe) and the exciting laser pulse (pump). In our setup, the problem of space charge effect was ameliorated by compressing 90 keV photo-emitted electron pulses using a radio-frequency electric field. The compression allowed us to increase the beam current by almost two orders of magnitude higher than previously reported. We developed a laser-activated streak camera with a streak velocity of 1.89 mrad/ps to evaluate the compression by measuring the electron pulse duration in situ with a resolution of 100 fs. Electron pulses composed of half a million electrons with a duration of 350 fs were obtained. The velocity mismatch problem, on the other hand, was resolved by employing the technique of laser intensity front tilting. We also constructed a setup to measure the duration of the tilted front laser pulses by an interferometric technique. The timing between the pump and the probe was determined either by photo-ionization induced lensing of the electrons in the gas for normal front laser pulses, or by a transient space charge/surface polarization creation in a copper foil that deflected the electron pulses. The change in the timing between the laser and the electrons was measured by the streak camera with a resolution of 70 fs RMS. ^
Molecular physics|Atomic physics|Optics
Zandi, Omid, "Design and Construction of a High-Current Femtosecond Gas-Phase Electron Diffraction Setup" (2017). ETD collection for University of Nebraska - Lincoln. AAI10683670.