[PAST EVENT] Zhaozhu Li: Physics Dissertation Defense
Photocathodes play an important role in present large accelerator facilities by providing polarized or un-polarized electron beams. Current state-of-art photocathodes consist of semiconductor super-lattice GaAs/GaAsP for polarized electrons with quantum efficiency ~1% and polarization ~90% at near-infrared wavelength for the incident light. Despite the advantages offered by metallic photocathodes regarding longer life time, fast response time and low requirements of ultra-high vacuum environment, they have not been put to use due to their low quantum efficiency, even though one can envision several approaches to achieve spin-polarization from them. A possible solution is to apply the Fano resonance, that involves coupling the surface plasmon resonance and the 1st diffraction order of incident light on a corrugated silver surface. This thesis demonstrate that this approach yields an enhancement effect of the QE performance of a cesiated silver grating cathode for light incident at the resonance angle compared to that of a cesiated flat silver cathode measured in the same system. By further altering the grating profile through oblique angle deposition (OAD) of a silver thin film onto a grating surface using magnetron sputtering deposition, one can further enhance the Fano resonance and consequently improve the electric field intensity near the silver cathode surface. Ensuing QE measurement confirm an enhancement of QE (26%) on the cesiated OAD sample comparing to a cesiated one obtained under normal deposition(ND) for light incident at resonance, respectively, showcasing a possible venue for metallic photocathodes for this application.
Bio: Zhaozhu Li was born in Qiqihar, Heilongjiang, China. She developed a special interest in Physics since she was a teenager. She received her B.S. in 2009 and began her pursuit of advanced studies of Physics at William & Mary in that same year. She joined Professor Lukaszew?s group in 2011 and has been working on plasmonic approaches for silver-based photocathodes.