Two-colour operation and applications of the CLIO FEL in the mid-infrared range

The two-colour operation of an FEL has been demonstrated a few years ago with the CLIO infrared free-electron laser, but the intracavity Brewster plate used for laser extraction did not allow to lase at wavelengths larger than 15 μm, and the two-colours separation could not be larger than λ1–λ2=1 μm. Recently, we have achieved two-colour operation with hole coupling, allowing a larger tuning range from 5 to 18 μm, and with a two-colour wavelength separation up to λ1–λ2=5 μm. A pump/probe application experiment has been performed with the two colours, and this is the best demonstration of the stability and reliability of the two-colour laser operation.