High Spin Polarization and High Brightness Electron Source

Abstract

A compact review of our research activities to improve various beam performances of spin polarized electron source, such as, 1) spin polarization, 2) quantum efficiency, 3) peak current density, 4) brightness, 5) beam energy resolution, 6) response time, and 7) NEA surface life time is given. In particular, our efforts toward higher brightness and high spin polarization electron source or LEEM using transmission photocathode are described in detail. The achievements are summarized as follows: A 20-keV gun was constructed with a transmission photocathode including an active layer of a GaAs-GaAsP superlattice. The photocathode illuminated by laser light with a spot diameter as small as 1.3 μm and a brightness of ∼2×107 A·cm−2·sr−1 (a reduced brightness of ∼1.0×107 A·cm−2·sr−1·V−1) and a peak polarization of ∼90% were achieved at the same time for an extracted current of 5.3 μA. This brightness is still one order magnitude smaller than those of the W-field-emitters, but one order higher than those of LaB6 emitters and three orders than those of conventional polarized electron sources.