Temporal stability of the UVOR-FEL micropulse

Optical cavity and control system of the UVSOR-FEL have been newly develope d to improve performances and to obtain better availability for user applic ation experiment. Lasings at visible and UV wavelength regions were success fully obtained in test experiments. By optimizing reflectivity and transmis sion of cavity mirrors, an average out-coupled power of more than 15 mW was achieved at a wavelength of 270 nm. Though a CW lasing zone at the top of a detuning curve was clearly obtained, an oscillation of FEL micropulse tim e jitter with 60 Hz appeared, which is probably due to a mechanical vibrati on of the cavity mirror caused by "sound noise" of the environment. Observe d macrotemporal structure has been examined by a computer simulation includ ing both effects of the mirror oscillation and the cavity length detuning. Results suggest that the mirror vibration should be reduced to less than 0. 1 mu m to suppress the amplitude of the time jitter comparable to an intrin sic temporal width of the FEL micropulse. (C) 2000 Elsevier Science B.V. Al l rights reserved.