BROAD-BAND TUNABILITY OF A FAR-INFRARED FREE-ELECTRON LASER

A unique property of the free-electron laser (FEL) is its capability t o be tuned continuously over a wide spectral range. This is a major di fference with all other high-power lasers. However, the tunability of first-generation FELs used to be quite poor (typically 10% or less), d ue to constraints imposed by the accelerator and the undulator. The fr ee electron laser for infrared experiments (FELIX) uses an undulator w ith an adjustable gap, which permits wavelength scans over an octave i n typically 2 min without the need for any readjustment of the electro n beam. Results obtained in operation of the long-wavelength FEL of th e FELIX facility are presented. These involve measurements of the spec tral range covered (16-110 mum), the output power, and the influence o f the cavity desynchronism. The results are compared with numerical si mulations.