TUNABILITY AND POWER CHARACTERISTICS OF THE LEBRA INFRARED FEL

The use of the infrared (IR) Free-Electron Laser (FEL) in medical science and material science started in October 2003 at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University. The FEL resonator which consists of silver-coated copper mirrors has demonstrated a wavelength tunability ranging from 0.9 to 6.5 µm as a function of the electron energy and the undulator K-value. The wavelength dependence of the FEL output power has been measured in terms of different electron energies and different undulator K -values. At about 2 µm, an FEL energy of roughly 25 mJ/macropulse has been obtained at the FEL monitor port, which corresponds to the peak power of 1 to 2 MW, provided that the FEL pulse length is less than 0.5 ps that resulted from the measurement by the autocorrelation method. A power decrease observed in the long-wavelength range has resulted from the wavelength dependence of the coupling coefficient of the FEL resonator mirror and the transport efficiency of the FEL guiding optics.