title: First Observation of z-Dependent Electron-Beam Microbunching Using Coherent Transition Radiation.
abstract: We report the first measurements of the electron-beam microbunching z dependence in a self-amplified spontaneous-emission (SASE) free-electron laser (FEL) experiment by the observation of visible wavelength coherent transition radiation (CTR). In this case the fundamental SASE wavelength was at 537 nm, and the CTR exhibited an exponential intensity growth similar to the SASE radiation. In addition, we observed for the first time structure in the CTR angular distribution patterns that may be useful for optimizing SASE FEL performance.
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439.
authors.initials: AH
authors.lastname: Lumpkin
authors.initials: R
authors.lastname: Dejus
authors.initials: WJ
authors.lastname: Berg
authors.initials: M
authors.lastname: Borland
authors.initials: YC
authors.lastname: Chae
authors.initials: E
authors.lastname: Moog
authors.initials: NS
authors.lastname: Sereno
authors.initials: BX
authors.lastname: Yang