Characteristics of a Ta photocathode for the generation of picosecond x-ray pulses

The properties of laser-driven tantalum photocathodes as an electron emitter for the creation of ultrashort electron bunches and x-ray pulses are discussed. Despite the smaller quantum efficiency of metals, their inertness, damage threshold, and lifetime compare favorably with semiconductor photocathodes. Using the fourth harmonic of a Nd:YAG laser, currents of over 3 nC per pulse have been achieved which produced x-ray pulses with a brightness of 6.2×106 Cu Kα x-ray photons cm−2 sr−1 and a duration of 70 ps, as determined by an x-ray streak camera.