Sokendai, Ibaraki, Japan
KEK, Ibaraki, Japan
LAL, Orsay, France
Waseda University, Tokyo, Japan
Laser-Compton scattering has become an important technique for beam diagnostics of the latest accelerators. In order to develop technologies for low emittance beams, 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 are developing a new type of beam profile monitor which works on the principle of inverse Compton scattering between electron and laser light. In order to achieve effective collision of photon and electron, a pulsed and very thin size laser is required. Laser wire is one technique of measuring a small beam size. With green lasers, which are converted to second harmonics from IR pulsed laser, minimum beam waist is half of the beam waist obtained using infrared (IR) laser oscillator. Therefore, it is possible to obtain beam waist less than 5 μm 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 pulsed IR laser is converted to second harmonics with a non-linear crystal. Pulsed green laser is injected inside four mirror optical cavity to obtain very small beam waist at interaction point (IP). Using a pulsed compact laser wire, we can measure 10 um electron beams in vertical directions. We report the development of the pulsed green laser and parameters of compact four mirror optical cavity for effective inverse Compton scattering.
