Progress report on the ELSA FEL and first lasing

Abstract The ELSA free-electron laser has delivered its first FEL photons at a wavelength of about 23 μm. Electron bunches were produced by a 144 MHz photoinjector, accelerated to 16.5 MeV by a 433 MHz linac and transported through a three-dipole U-turn into a 3.2 cm period hybrid undulator.