Pulsed green laser wire system for effective inverse compton scattering

Laser-Compton scattering has become an important technique for beam diagnostics of the latest accelerators. In order to develop technologies for low emittance beam, an Accelerator Test facility (ATF) was built at KEK. It consists of an electron linac, a damping ring in which beam emittance is reduced and an extraction line. For emittance measurement we developed a new type of beam profile monitor which works on the principle of Compton scattering between electron and laser light. In order to achieve effective collision of photon and electron, very thin size laser is required. Laser wire is one of such a technique to measure a small beam size. With green laser which is converted to second harmonics from IR pulsed laser, minimum beam waist is half of beam waist obtained using IR laser oscillator. Therefore, it is possible to obtain beam waist less than 5 value) using green laser pulse, which is required for effective photon-electron collision. First pulsed IR seed laser is amplified with 1.5 meter long PCF based amplifier system. This high power pulsed IR laser is converted to second harmonics with a non-linear crystal. Pulsed green laser is injected inside four mirror resonator to obtain very small beam waist at IP (Interaction Point). Using a pulsed compact laser wire, we can measure 5 m electron beam in vertical direction. From observed Compton signal profile, bunch length of electron beam is measured as 23.3±0.7 ps. Electron beam size in vertical plane is measured as 12.6±1.8 μ and vertical emittance is measured as 24.1± 6.8 pm-rad. Longitudinal bunch length and vertical beam size of electron beam was measured with pulsed laser wire system. We report the development of high power pulsed green generation and compact four mirror resonator parameters for effective Inverse-Compton scattering in this paper.