Photocathode Investigation for Ultrafast Electron Microscopy

Ultrafast transmission electron microscopes (UEM) have provided scientists the ability to investigate materials dynamics on the nanometer femtosecond spatiotemporal scale, leading to many new scientific discoveries. After starting as highly specialized tools, these instruments are becoming more and more common throughout the world as companies work to make them commercially available and institutions recognize their value. While new operating concepts are being developed [1], typical UEMs in operation utilize a photocathode to produce short bursts of electrons. The community has not coalesced around a single photocathode design, with a variety of geometries and materials being employed [2-4]. While this is partly due to differing needs in terms of coherence, number of electrons per pulse, etc., there is an active field of research trying to determine the best design for photocathodes in UEM, the performance of which is generally the limiting factor in the instruments’ resolutions. Here we investigate one such photocathode design, the “guard ring” cathode.