Infrared (IR) vs. X-ray power generation in the SLAC Linac Coherent Light Source (LCLS)

The LCLS, a free-electron laser (FEL) designed for operation at a first harmonic energy of 300 eV (λ≈40 Å) in the self-amplified spontaneous emission regime, will utilize electron bunches compressed down to durations of < 0.5 ps, or lengths of < 150 μm. It is natural to inquire whether coherent radiation of this (and longer) wavelength will constitute a significant component of the total coherent output of the FEL. In this paper a determination of a simple upper bound on the IR that can be generated by the compressed bunches is outlined. Under the assumed operating parameters of the LCLS undulator, it is shown that the IR component of the coherent output should be strongly dominated by the X-ray component