Ultrafast electron microscopy: Instrument response from the single-electron to high bunch-charge regimes

• DOI: 10.1016/j.cplett.2017.01.055
• Publication Date: 2017-01-25T07:18:41Z
• Authors: Dayne A. Plemmons; David J. Flannigan
• Keywords: 0301 basic medicine; 03 medical and health sciences

Abstract We determine the instrument response of an ultrafast electron microscope equipped with a conventional thermionic electron gun and absent modifications beyond the optical ports. Using flat, graphite-encircled LaB 6 cathodes, we image space-charge effects as a function of photoelectron-packet population and find that an applied Wehnelt bias has a negligible effect on the threshold levels (>10 3 electrons per pulse) but does appear to suppress blurring at the upper limits (∼10 5 electrons). Using plasma lensing, we determine the instrument-response time for 700-fs laser pulses and find that single-electron packets are laser limited (1 ps), while broadening occurs well below the space-charge limit.