Photoemission studies of yttrium photocathodes by using the visible radiation

The present work reports on Yttrium based photocathodes. A Yttrium (Y) thin film is deposited via pulsed laser deposition (PLD) on the copper (Cu) back flange of a radio frequency (rf) gun for photocathode application. Because of a lower work function with respect to Cu, Y photocathodes are particularly appealing for the possibility to illuminate them with visible laser pulses, with the advantage of a higher energy per pulse, paving the way to high repetition rate photoinjectors, driven by conventional laser sources. In addition, working at λ ∼ 400 nm the small energy difference between the Y work function (about 3 eV) and the laser photon energy reduces the contribution of the intrinsic emittance of the material. Photoelectrons, emitted by the thin film Y photocathode driven by the second harmonic of a Ti:Sapphire laser, have been characterized in terms of quantum efficiency and transverse emittance. Results have been compared with the theoretical ones obtained by the three-step model of Spicer for metallic photocathodes.