OBSERVATION OF HIGHER HARMONICS IN THE NIJI-IV FEL

Characteristics of higher harmonics from the optical klystron have bee n investigated to study the feasibility of the coherent harmonic gener ation (CHG) as a useful method to shorten the FEL wavelength down to t he vacuum ultraviolet (VUV) in a small-scale storage ring like the NIJ I-IV. Obvious modulation was observed on the 3rd harmonic line at 117 nm with a VUV monochromator. The 5th and 7th harmonics with reasonable intensity were also observed by using a real-time spectrum measuremen t system. These facts suggest that coherent photons are obtainable at the VUV wavelength down to similar to 50 nm through the CHG process by introducing a high power external laser or utilizing the intense intr a-cavity optical field in the visible FEL as a source for electron bun ching in the optical klystron. (C) 1998 Elsevier Science B.V. All righ ts reserved.