Generation of GW - level , sub - Angstrom Radiation in the LCLS using a Second - Harmonic Radiator ∗

Electron beams are strongly microbunched near the high-gain free-electron laser (FEL) saturation with a rich harmonic content in the beam current. While the coherent harmonic emission is possible in a planar undulator, the thirdharmonic radiation typically dominates with about 1% of the fundamental power at saturation. In this paper, we discuss the second-harmonic radiation in the Linac Coherent Light Source. We show that by a suitable design of an secondstage undulator with its fundamental frequency tuned to the second harmonic of the first undulator, coherent second-harmonic radiation much more intense than the third-harmonic is emitted. Numerical simulations predict that GW-level, subAngstrom x-ray pulses can be generated in a relatively short second-harmonic radiator. Presented at the 26 International Free-Electron Laser Conference and 11 FEL User Workshop (August 29 September 3, 2004, Trieste, Italy) ∗Work supported by Department of Energy contract DE–AC02–76SF00515. †Email: [email protected] Generation of GW-level, sub-Angstrom Radiation in the LCLS using a Second-Harmonic Radiator ∗ Z. Huang† , SLAC, Stanford, CA 94309, USA S. Reiche, UCLA, Los Angeles, CA 90095, USA