Lasing down to the deep UV in the NIJI-IV FEL

Lasing has been obtained at the wavelengths down to the deep UV on the NIJI -IV free electron laser (FEL) system. The shortest wavelength obtained was 228 nm and the laser peak power was estimated to be similar to 200 and simi lar to 40 mW at 300 and 240 nm, respectively. Suppression of the fast head- tail instability in the electron beam led to a drastic enhancement in the l aser gain which enabled us to achieve such short-wavelength lasing even in a compact storage ring such as NIJI-IV. Low-loss cavity mirrors having Al2O 3/SiO2 dielectric layers are being prepared to obtain FEL operation at much shorter wavelengths. (C) 1999 Elsevier Science B.V. All rights reserved.