Computational and Experimental Characterization of High-Brightness Beams for Femtosecond Electron Imaging and Spectroscopy
AbstractUsing a multilevel fast multipole method, coupled with the shadow imaging of femtosecond
photoelectron pulses for validation, we quantitatively elucidate the photocathode, space charge,
and virtual cathode physics, which fundamentally limit the spatiotemporal and spectroscopic
resolution and throughput of ultrafast electron microscope (UEM) systems. We present a simple
microscopic description to capture the nonlinear beam dynamics based on a two-fluid picture and
elucidate an unexpected dominant role of image potential pinning in accelerating the emittance
growth process. These calculations set theoretical limits on the performance of UEM systems and
provide useful guides for photocathode design for high-brightness electron beam systems.
J. Portman, H. Zhang, Z. Tao, K. Makino, M. Berz, P.M. Duxbury, C.-Y. Ruan,
Applied Physics Letters 103 (2013) 253115
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