Laser Focusing System for High Brightness Polarized Electron Source for SPLEEM

For construction of a high brightness polarized electron source for SPLEEM (Spin Polarized Low Energy Electronic Microscope), a new transmission type photocathode has been developed at Nagoya Univ. In our scheme, a laser light is injected from backside of the photocathode and an electron beam is emitted forward from the surface. A high numerical aperture lens with a short focal length can focus the laser lights into a small spot of photocathode. A laser spot with a diameter of 2.2μm could be achieved by our laser system, and it contributed to realize the high beam brightness of 105A⋅cm−2⋅sr−1 or more for a total current of 5μA.