Roger J. Dejus

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Self-amplified spontaneous emission in a free-electron laser has been proposed for the generation of very high brightness coherent x-rays. This process involves passing a high-energy, high-charge, short-pulse, low-energy-spread, and low-emittance electron beam through the periodic magnetic field of a long series of high-quality undulator magnets. The(More)
The Undulator A at the Advanced Photon Source (APS) is a planar permanent magnet hybrid device optimized for generating x-rays from 3 keV to 45 keV by using the first, third, and fifth radiation harmonics. It also produces x-rays above this energy. For high-energy experiments, users are relying on using higher harmonics, which has become possible because of(More)
The Linac Coherent Light Source (LCLS) undulator line will consist of undulator segments separated by breaks of various lengths. Focusing quadrupoles, in a FODO lattice, and electron-beam diagnostics will be located in the breaks, and every third break will be longer to also accommodate photon diagnostics. The electron-beam beta function and the undulator(More)
The linear integral equation based computer code (RON: “Roger Oleg Nikolai”), which was recently developed at Argonne National Laboratory, was used to calculate the self-amplified spontaneous emission (SASE) performance of the free-electron laser (FEL) being built at Argonne. Signal growth calculations under different conditions are used for estimating(More)
We report the first measurements of z-dependent coherent optical transition radiation (COTR) due to electron-beam microbunching at high gains ( >10(4)) including saturation of a self-amplified spontaneous emission free-electron laser (FEL). In these experiments the fundamental wavelength was near 530 nm, and the COTR spectra exhibit the transition from(More)
The nonlinear generation of harmonics in a self-amplified spontaneous emission (SASE) free-electron laser (FEL) continues to be of interest. Complementary to such studies is the search for information on the electron beam microbunching harmonic components, which are revealed by coherent optical transition radiation (COTR) experiments. An initial z-dependent(More)
The considerable intensity of Advanced Photon Source (APS) undulator A as a source of high-energy X-rays permits the performance of numerous types of experiments that require such photon energies. Measured and calculated properties, in the 50-200 keV range, of the X-ray beam from undulator A, installed in sector 1 of the APS, are presented. The flux spectra(More)
A request was made by a user group at the Advanced Photon Source to provide a design of an undulator generating intense hard x-rays over a limited photon energy range (12 – 15 keV), with very small x-ray “contamination” at higher energies. For their scientific program (and technique used), the x-ray images obtained are sensitive to inherent imperfections in(More)
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