CLIO, an infrared free electron laser facility

The ''CLIO'' Free Electron Laser is a tunable infrared laser that is principally dedicated to users. This laser uses a 30-60 MeV relativistic electron beam, provided by a linear accelerator, and an undulator to provide the optical gain needed for the laser process. This facility has been operating since January 1992, producing laser pulses of about 10 MW in 2 ps, with a tunable wavelength range of 2 to 17.5 μm. The average power depends on the repetition rate of laser pulses, and presently reaches about 2 W (at 1/4 of the maximum repetition rate). Four user rooms are available for general experiments using the CLIO laser beam. Three experiments have already succesfully taken place. Study of two photons absorbtion in InSb and InAs as a function of wavelength; infrared microscopy by tunnelling effect, by peaking the evanescent wave of the laser probe on a sample with an optical fiber, for different wavelengths; and surface spectroscopy using the ''Sum Frequency Generation'' technique, i.e. by mixing the tunable CLIO infrared laser with a synchronized Nd-Yag laser in order to observe the resonance vibration on a surface. This paper presents the general performances of the accelerator, of the laser and describes the principal application experiments which are now in progress. (orig.)