Picosecond and sub-picosecond pulsed laser deposition of Pb thin films

Pb thin films were deposited on Nb substrates by means of pulsed laser deposition (PLD) with UV radiation (248 nm), in two different ablation regimes: picosecond (5 ps) and subpicosecond (0.5 ps). Granular films with grain size on the micron scale have been obtained, with no evidence of large droplet formation. All films presented a polycrystalline character with preferential orientation along the (111) crystalline planes. A maximum quantum efficiency (QE) of 7.3×10 - 5 (at 266 nm and 7 ns pulse duration) was measured, after laser cleaning, demonstrating good photoemission performance for Pb thin films deposited by ultrashort PLD. Moreover, Pb thin film photocathodes have maintained their QE for days, providing excellent chemical stability and durability. These results suggest that Pb thin films deposited on Nb by ultrashort PLD are a noteworthy alternative for the fabrication of photocathodes for superconductive radio-frequency electron guns. Finally, a comparison with the characteristics of Pb films prepared by ns PLD is illustrated and discussed.