Discrete space charge aberrations in spherical photoelectric emission structures

Abstract

Concentric spherical photoelectron diode structures can be used to generate high current densities when illuminated with intense laser beams. For applications in electron microscopy and for beam source applications, trajectory aberrations of the emitted particles are important. This paper describes Monte Carlo estimations of trajectory fluctuations produced by discrete-charge interactions in a laser-driven spherical photoemission structure. The trajectory of one photoelectron traveling in the presence of 125 randomly positioned neighbors is computed, and its apparent source position is determined as it arrives at the anode. Hundreds of such passes are averaged to estimate the aberration. Apparent source blur sizes range between 1 nm and 3.5 µm, for emitter radii between 160 µm and 2.82 mm, as the current density increases from 1 to 1000 A/cm2. Such small aberrations imply that discrete space charge effects do not significantly degrade the performance of these electron sources under most conditions.