Photoemission studies on LaB6 and pure metals using a nanosecond KrF excimer laser

The CAEP RF accelerator will use a photocathode rf gun to provide a high brighness electron beam for FEL experiments. To achive long lifetime, our photocathode development initially concentrates on LaB6 and some pure metals. We report experiments on these materials with a pulsed KrF excimer laser. Using surface heating and laser cleaning (surface activation), the quantum efficiency is dramatically enhanced. The quantum efficiencies of LaB6, Y, Ag and Al are about 6.1 × 10−4, 3.8 × 10−4, 2.8 × 10−4, and 1.4 × 10−4, respectively. Using the pepper pot method, the nomalized beam emittances for these materials are about 10 π mm mrad and the corresponding normalized brightnesses are about 1010 A/m2 rad2. These photocathodes will be tested on the 1 + 1/2 cell microwave cavity at CAEP.