Untangling the Contributions of Image Charge and Laser Profile for Optimal Photoemission of High-Brightness Electron Beams
AbstractUsing our model for the simulation of photoemission of high brightness electron
beams, we investigate the virtual cathode physics and the limits to
spatio-temporal and spectroscopic resolution originating from the image charge
on the surface and from the profile of the exciting laser pulse. By contrasting
the effect of varying surface properties (leading to expanding or pinned image
charge), laser profiles (Gaussian, uniform, and elliptical), and aspect ratios
(pancake- and cigar-like) under different extraction field strengths and
numbers of generated electrons, we quantify the effect of these experimental
parameters on macroscopic pulse properties such as emittance, brightness (4D
and 6D), coherence length, and energy spread. Based on our results, we outline
optimal conditions of pulse generation for ultrafast electron microscope
systems that take into account constraints on the number of generated electrons
and on the required time resolution.
J. Portman, H. Zhang, K. Makino, C.-Y. Ruan, M. Berz, P. M. Duxbury,
Journal of Applied Physics 116 (2014) 174302
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