Two-colour operation of a Free-Electron Laser and applications in the mid-infrared

The two-colour operation of a Free-Electron Laser (FEL) has been demonstrated with the "CLIO" infrared facility. A two section undulator allows the production of picosecond laser pulses at two different wavelengths lambda(1) and lambda(2) simultaneously, in a wavelength range from lambda = 5 mu m to lambda = 18 mu m, and with a wavelength separation of two colours of up to lambda(1) - lambda(2) = 5 mu m. The time overlap. between both colours, has been measured on a picosecond time scale and on a microsecond time scale. An initial pump-probe application experiment has been performed with the two colours: stimulated emission has been measured in a 3-level Quantum-Well system. This is the best demonstration of the stability and reliability of the two-colour laser operation.