A simplified description of X-ray free-electron lasers

J. Synchrotron Rad. (2011). 18, 101-108 (doi.org/10.1107/S090904951004896X)

Can the working mechanism of free-electron lasers (FELs) be understood with basic arguments and simple mathematics? The question is relevant because of the recent commissioning of the first X-ray FEL and the fast progress in this field. The answer is positive: we derive the basic FEL equations - including gain and saturation properties - with elementary arguments. We explain, in particular, the counterintuitive fact that electron microbunching with the very short periodicity required for X-rays is much more difficult than for long-periodicity infrared FELs.