Superlattice NEA photocathode and gun technology developed for high polarization and low emittance electron beam

The performance required for PES (Polarized Electron Source) is dependent on variety of accelerators and physics experiments. Usually following items are included; 1) high polarization, 2) high quantum efficiency, 3) high peak current for a pulse beam, 4) high average current for a CW beam, 5) sub-nanosecond multi-bunch structure for a future ILC (international linear collider) beam, 6) long cathode-lifetime and 7) low beam emittance. Here, technologies developed to improve these performances are briefly reviewed. In addition, further applications of NEA-GaAs photocathode gun, such as ERL (Energy Recovery Linac) or SPLEEM (Spin Polarized Low Energy Electron Microscopy) are discussed. (author)