CHARACTERISTIC IMPROVEMENT OF TUNGSTEN PHOTOCATHODE BY TWO-WAVELENGTH IRRADIATION OF THE ND:YAG LASER

Metals or metal compounds as photocathodes provide high current density and have a high damage threshold for laser irradiation. In addition, the quantum efficiency of these cathodes is enhanced by heating to a higher operating temperature. The tungsten photocathode heated up to 1400 K and irradiated by 2ω (532 nm) of the Nd:YAG laser produced an electron beam with high current density (∼1 kA/cm2) and the quantum efficiency was about 10−5. The fundamental (1064 nm) of a Nd:YAG laser was used to further heat up the cathode instantly; the temperature rise was calculated to be 2000 K in a 10 ps time scale. Compared to the static 1400 K operation, two times enhancement of quantum efficiency was observed.