Stability of the LEBRA infrared FEL

Abstract The free electron laser (FEL) gain and the power have still been unstable, although the lasing of 1.5 μm FEL was achieved at the Laboratory for Electron Beam Research and Application (LEBRA). It has been observed that the FEL gain changes during the pulse duration. In order to investigate the cause of the fluctuation of the FEL gain, the beam energy spectra in the pulse duration and the IR light signals were measured with different input RF power and RF phase of the injector. It is found that the fluctuation of the beam energy during the pulse duration occurs in spite of the RF phase flatness (