A comparison between the fundamental and third harmonic interactions in X-ray free-electron lasers

Free-electron lasers are under study as 4th generation light sources for 1.5 إ X-rays. However, the interaction is extremely sensitive to the beam quality, and it is useful to consider alternate schemes. The scheme discussed here is to generate 4.5 إ X-rays using the fundamental interaction and rely on nonlinear 3rd harmonic generation to reach 1.5 إ. The specific example discussed corresponds to the Linac Coherent Light Source proposed at the Stanford Linear Accelerator Center.