Evolution of Spectral Structure in the Storage Ring Free Electron Laser Micropulse

Abstract

We observed the evolution of the spectral structure in storage ring free electron laser (SRFEL) micropulses on the compact storage ring NIJI-IV. As in the pulse width and pulse structure of the SRFEL micropulse, it was clarified that a macrotemporal structure existed in the line width and spectrum of the SRFEL micropulse. When longitudinal overlapping between an electron bunch and an optical pulse was almost perfect, the wavelength and spectral line width of the SRFEL were extremely steady, although the intensity of the SRFEL was unstable. A pulse structure is usually measured using a streak camera with a fast sweep to investigate the characteristics of the micropulse. However, it was clarified that the characteristics of the micropulse could be estimated by observing the evolution of the micropulse spectrum with a slow time resolution of 0.1 ms. The evolution of the spectra in the SRFEL micropulses for a two-color oscillation mode was also observed. Enhancement of the two lasing wavelengths was observed in a macropulse mode.