Intense ultrashort pulse generation using the JAERI far-infrared free-electron laser

Nagai, Ryoji; Hajima, Ryoichi; Nishimori, Nobuyuki; Kikuzawa, Nobuhiro ; Sawamura, Masaru; Minehara, Eisuke

An intense ultrashort pulse is generated at the perfect synchronism of optical-resonator length in the JAERI far-infrared free-electron laser. At wavelength of 22.5 m, second-order optical autocorrelation measurements show that the FEL pulse duration is 250 fs and less than four optical cycles which is consistent with numerical calculation result. The pulse energy ranges up to 100 J. The second-hermonic generation in a 2 mm thickness Te crystal is used to provide the nonlinear autocorrelation signal. In the various desynchronism of optical-resonator length, the way of appearing of the sub-pulse corresponded to the calculation result well, too.