Coherence of a spin-polarized electron beam emitted from a semiconductor photocathode in a transmission electron microscope

Abstract

The brightness and interference fringes of a spin-polarized electron beam extracted from a semiconductor photocathode excited by laser irradiation are directly measured via its use in a transmission electron microscope. The brightness was 3.8 × 107 A cm−2 sr−1 for a 30-keV beam energy with the polarization of 82%, which corresponds to 3.1 × 108 A cm−2 sr−1 for a 200-keV beam energy. The resulting electron beam exhibited a long coherence length at the specimen position due to the high parallelism of (1.7 ± 0.3) × 10−5 rad, which generated interference fringes representative of a first-order correlation using an electron biprism. The beam also had a high degeneracy of electron wavepacket of 4 × 10−6. Due to the high polarization, the high degeneracy and the long coherence length, the spin-polarized electron beam can enhance the antibunching effect.

Ultrafast transmission electron microscopy using a laser-driven field emitter: Femtosecond resolution with a high coherence electron beam

“…Over the last decade, various approaches have been undertaken to enhance the beam quality of ultrafast electron sources for time-resolved experiments, including a tailoring of photoemission laser wavelength [57], photocathode workfunctions and materials [58][59][60], as well as photoemission spot sizes [61,62], and by enhanced extraction fields in radio-frequency cavities [10] and at sharp emitter needles [20]. Also alternative approaches using cold atomic gases are pursued [63][64][65].…”

Effects of ion bombardment on bulk GaAs photocathodes with different surface-cleavage planes

“…GaAs photocathodes are used to generate spin-polarized electron beams for nuclear and particle physics research [1]. More recently, these photoguns have found application in material science where spin-polarized electron beams can be used for magnetization-sensitive imaging [2]. Direct current high voltage photoguns with GaAs [3,4] or alkaliantimonide photocathodes [5,6] are also used to produce bright electron beams for accelerator-based light sources.…”

Ultrafast electron microscopy for probing magnetic dynamics

“…Magnetic dichroism with electron orbital angular momentum post-selection [78][79][80][81][82] relies on similar mechanisms but has the potential for an adequate signal-to-noise ratio even with femtosecond pulses and kHz repetition rates. Spin-polarized transmission electron microscopy 83,84 may prove capable of both inelastic and elastic magnetic imaging.…”