Polarized pulsed beam source for electronic microscopy

A novel pulsed spin-polarized electron source is discussed. Unlike conventional devices based either on a thermionic cathodes or field-emission needle cathodes, the present source is based on photoemission. A gallium arsenide (GaAs) planar cathode impinged with a suitable circularly polarized laser can produce a polarized pulsed electron bunch with duration of the order of the laser pulse. Numerical simulations of the electron dynamics in the optimized cathode-anode geometry have shown that the beam with initial transverse size of a few mm can be focused down to 1 mum root-mean-square (RMS). The suggested source can, in principle, be installed on existing electron microscope thereby opening the path to time- resolved microscopy. Spin-polarization offers an effective probe for some magnetic phenomena. The design of the source and subsequent fabrication has been completed. In the present paper we discuss numerical studies of the source performance, its conceptual design, and report on the experimental status.