Electron emission from photo-cathodes for FEL

Summary form only given. Development of high-brightness photocathodes for a compact infrared free electron laser operated on LEENA (Laser Emitted ElectroN Accelerator) with a plane LaB/sub 6/ cathode and third harmonics of a mode-locked Nd:YLF laser (micropulse width: 10 psec, jitter: <1 psec) at LASTI/HIT was studied to enhance laser output. Photo-emission from the plane photocathodes of different materials such as LaB/sub 6/, W, DLC-W, Al, and AlN was measured with an aid of a focused Hg-lamp light and a band-pass filter. Before the measurement of electron emission the cathode was annealed for about 1 hour in the vacuum of <1.2/spl times/10/sup -9/ Torr. The power P of light on the cathode was measured with a power-meter (wavelength range: 200-1100 nm), where the light was filtered by the band-pass filter (range: 330/spl plusmn/100 nm). The electron emission current I/sub c/ was measured by a pico-ammeter. The cathode was biased at 2500 V. A gap between the cathode and the anode was 2 mm. The quantum efficiency was evaluated by dividing the emitted electron number per second N/sub c/ by irradiated photon number per second N/sub p/, where N/sub c/ was calculated from I/sub c/ and N/sub p/ was determined from P, a spectrum distribution of the Hg-lamp, transmittance of the low-pass filter, and power-meter sensitivity.