OPTICAL-PERFORMANCE OF THE CLIO INFRARED FEL

First laser oscillation on the CLIO infrared FEL was obtained in January 1992. This paper describes the layouts of the optical devices used for CLIO, and discusses the optical performances. This machine consists of an rf linear accelerator, described in a companion paper, providing a 30/70 MeV electron beam through a 48 period planar undulator (K = 0 to 2). The optical cavity is 4.8 m long and uses broadband metal mirrors. The optical beam is extracted with an intracavity CaF, or ZnSe plate. Laser oscillation has been obtained thus far in the range of lambda = 2.5 to 15 mum at accelerator energies of 32, 40 and 50 MeV. The average power of the laser is about 65 mW for the low duty cycle (6.25 Hz/32 ns) and up to 0.5 W for a duty cycle of 50 Hz/32 ns and should be 5-10 W at maximum repetition rate. The peak power extracted for 8 ps micropulses is 2.5 MW corresponding to 0.4% efficiency. Laser oscillation on the third harmonic of 10 mum has also been achieved (at lambda = 3.3 mum). Application experiments have already been done with the CLIO infrared laser (companion paper on nonlinear absorption in InSb), showing the good reliability and overall quality of the laser. The programme now is to operate the accelerator at other energies so as to cover the rest of the designed wavelength range (2-20 mum).