Development of Adaptive Feedback Control System of Both Spatial and Temporal Beam Shaping for Uv-laser Light Source for Rf Gun

We have been developing a stable and highly qualified UV-laser pulse as a light source for the rf gun, which is a potential injector for future light sources. Our gun cavity is a single-cell pillbox, and the copper inner wall is used as a photo cathode. At present, the short pulse energy stability of laser has been improved, with a reduction to 1.3~1.5% (rms) for third harmonic generation. In this improvement we only passively stabilized the system. We considered environmental controls in the clean room to reduce optical damage accidents and constructed a new humidity-controlled clean room in 2003. We then re-installed the entire laser system in this room in 2004. The relative humidity of this new clean room at room temperature is in the region of 50~60%, with a stability less than 2% (peak-to-peak). On the other hand, the ideal spatial and temporal profiles of a shot-byshot single-laser pulse are essential in order to suppress the emittance growth of the electron beam from an rf gun. This laser-shaping project has proceeded in two steps since its inception in 2002. In the first successful test run in 2002, with a microlens array as a simple spatial shaper, we obtained a minimum emittance value of 2π mm•mrad with a beam energy of 3.1 MeV, holding its charge to 0.1 nC/bunch. In the next test run in 2004, we prepared a deformable mirror for spatial shaping and a spatial light modulator based on fused-silica plates for temporal shaping. We are applying both types of adaptive optics to automatically shape both the spatial and temporal UVlaser profiles simultaneously with a feedback routine. We report here the principle and developing process of our laser beam quality control system.