SLAC, Menlo Park, California
LBNL, Berkeley, California
We present experimental studies of the gain length and saturation levels from 1.5 nm to 1.5 Å for a variety of conditions at the Linac Coherent Light Source (LCLS). By disrupting the FEL process with an orbit kick, we are able to measure the X-ray intensity as a function of the undulator length. This kick method is cross-checked with the method of removing undulator sections. We measure the FEL gain length as a function of X-ray wavelength, laser-heater induced energy spread, beta function and peak electron current. We also study the X-ray intensity level and FEL-induced electron energy loss after saturation as a function of undulator K value to determine the optimal taper. The experimental results are compared to analytical formulae and simulations.
ANL, Argonne
LBNL, Berkeley, California
Simulations of the x-ray free-electron laser (FEL) oscillator are presented that include transverse effects and realistic Bragg mirror properties with the two-dimensional FEL code GINGER. In the present cases considered, the radiation divergence is much narrower than the mirror acceptance, and the numerical algorithm can be simplified by ignoring the finite angular bandwidth of the mirror. In this regime GINGER shows that the saturated x-ray pulses have 109 photons and are nearly Fourier limited with peak powers in excess of 10 MW. We also include preliminary results for a four-mirror cavity that can be tuned in wavelength over a few percent, with future plans to incorporate the full transverse response of the Bragg mirrors into GINGER to more accurately model this tunable source.
ELETTRA, Basovizza
University of Nova Gorica, Nova Gorica
LBNL, Berkeley, California
The second stage of the FERMI FEL, named FEL-2, is based on the principle of high-gain harmonic generation and relies on a double-seeded cascade. Recent developments stimulated a revision of the original setup, which was designed to cover the spectral range between 40 and 10 nm. According to the numerical simulations we present here, the nominal (expected) electron-beam performance allows to extend the FEL spectral range down to 3 nm. A significant amount of power can be also expected at about 1 nm. We also show that the proposed setup is flexible enough for exploiting future developments of new seed sources, like, e.g., high harmonic generation in gases.