Gain narrowing of spectral and temporal widths in the UVSOR-FEL

Spectral and temporal widths of the UVSOR-FEL operated in a gain-switching mode have been experimentally studied. We measured time dependent evolution of the temporal width by using a dual-sweep streak camera. Time-resolved spectral width was also measured by a Fabry-Perot etalon and the slow sweep function of the streak camera. We have found that those widths are mostly determined in the beginning of the lasing process. The measured spectral and temporal widths at various beam currents are in good agreement with theoretical calculations of the gain narrowing model.