The Low-Energy Undulator Test Line: A SASE FEL Operating from 660 to 130 nm

There is a strong desire for short wavelength (down to 1 Å), short pulsewidth (<100 fs), high‐brightness, transverse, and longitudinally coherent light pulses for use by the synchrotron radiation community. Much effort is ongoing worldwide to advance this desire both experimentally, in theory and design, and politically. One of the ongoing experimental efforts is the low‐energy undulator test line (LEUTL) at the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). This experiment is based upon the self‐amplified spontaneous emission (SASE) process, a method to attain a next‐generation light source. This presentation gives an overview concerning the history and results of next‐generation light sources, the results of the LEUTL SASE FEL, and the description of the upcoming first user experiment on LEUTL. We will also briefly review exotic schemes for future, next‐generation light sources based upon FELs including biharmonic undulators and the possibility of interfacing of traditional x‐ray lasers with FELs.