Developments of high brightness needle photo-cathode for free electron laser

Summary form only given. A high-brightness needle photo cathode, being developed for a compact infrared free electron laser for industrial application is studied. A free electron laser operation on LEENA (Laser Emitted ElectroN Accelerator), 6 MeV small Linac at LASTI/HIT was demonstrated with plane LaB/sub 6/ cathode driven by third harmonics of mode-locked Nd: YLF laser. Experimental results and analytic calculations show that the electron beam quality is the major limit to generating sufficient high power FEL output using a compact linac such as LEENA. We are planning to use a high-field needle (tungsten or molybdenum) photo-cathode as a candidate for a new electron gun to improve beam energy spread, beam current and beam emittance. A preliminary experiment on the field-emission tungsten-needle-cathode was performed. Current and voltage properties were in good agreement with Fowler-Nordheim field-emission theory. This result show that generation of high peak current beam of about 10 A is possible by applying 10 to 20 kV on to a needle with diameter less than 1 micron. Matching with a linac may be achieved by the photo-emission mode.