We developed a metallic photocathode to produce a high-brightness electron beam for freeelectron lasers. Single crystalline lanthanum hexaboride had a quantum yield exceeding 10-4 at 1000 °C with a frequency-tripled Nd: YAG laser. A tungsten cathode, irradiated by a frequency-doubled Nd: YAG laser, emitted photo-electrons through the two-photon process. The quadratic dependence of the photo-current on the laser intensity could improve the low quantum yield of the multi-photon process. This tungsten photocathode is capable of generating an 1 kA/cm2 electron beam. Futher, heating of these materials could increase the quantum yield. With this technique, these cathodes will generate an electron beam, which has normalized brightness more than 1011A/m2/rad2, in a radio-frequency electron gun.
