<title>Start-up of lasing in compact far-infrared free-electron laser driven by 8-MeV microtron</title>

Abstract

We have developed a compact Far Infrared Free Electron Laser (FIR FEL) on the base of 8 MEV microtron, which can provide 6 microsecond(s) up to 70 mA macropulse beam current. Beam line consists of bending and steering magnets. Optical Transition Radiation screen and 3 doublets of quadruples to provide matching of microtron output electron beam parameters with optimized parameters for FEL operation. A 2 m length, 25 mm period and 5.7 mm gap undulator has extremely low field error of 0.05% for the magnet field peak amplitude in the range 5.5 - 6.5 kG. Inside the undulator the electron beam passes through 2 mm X 20 mm aperture 2779 mm length planar waveguide. On both sides of the waveguide are installed two cylindrical 3 m curvature mirrors. They form confocal type free space mode in horizontal plane and waveguide mode in vertical plane of the optical resonator. A hole in output mirror provides coupling ratio about 1 - 2%. During experiments we have observed the coherent effect in spontaneous emission with power enhancement approximately 1000 times. It was observed too the long wave radiation, which can be explained by vertical betatron oscillation of electrons in undulator. The experiments with FIR resonator and Ge-Ga liquid He cooled detector shown coherent generation and tunability of it power with tuning of the length of the resonator. The enhancement of outcoupled signal in 50 times was detected with changing of resonator length. This phenomenon can be explained as startup of the lasing process in FIR resonator.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.