Free-electron lasers sources for scientific applications

The free-electron laser ("FEL") has proven to be an invaluable source of ra diation in the UV to far infrared spectral ranges. It is based on the ampli fication of an optical wave by a high energy electron beam oscillating tran sversely to its propagation. In the last decade, several FELs have been des igned and built as user dedicated facilities. Presently, seven infrared FEL s, such as CLIO at Orsay (France), are running more than 1000 hours/year fo r users performing experiments in various scientific fields. In the UV spec tral range, the Super-AGO (Orsay, France) FEL is promoting applications in various fields. The main applications are described and prospects are given .