Measurements of exponential gain and saturation of SASE at the APS LEUTL

The possibility of using self-amplified spontaneous emission (SASE) to achieve a peak X-ray brightness nearly 11 orders of magnitude greater than available at today´s third-generation light sources has in recent years generated tremendous excitement in the synchrotron light source community. With continued refinement in electron beam sources, electron beam control and metrology, and undulator magnet technology, this dream is rapidly approaching reality. The Advanced Photon Source (APS) Low-Energy Undulator Test Line (LEUTL) free-electron laser (FEL) project is designed to explore the SASE process in the visible through vacuum ultraviolet spectral range, the current limit of the technology. At present we have made measurements of the SASE process at 530 nm and 385 nm. We will present these measurements, in particular the growth of quantities such as intensity, spectrum, and microbunching along the length of the undulator. Measurements of these properties at and beyond the saturation point will also be presented. The experimental measurements will then be compared with theory and simulation