WEP001

The test-accelerator as coherent terahertz (THz) source (t-ACTS) has been routinely producing short electron bunches at the Research Center for Accelerator and Radioisotope Science (RARiS), Tohoku University. According to a theoretical consideration of the pre-bunched Free Electron Laser (FEL) technique, it is expected to produce the THz radiation with extremely high electric fields exceeding 10 MV/cm. In order to achieve the pre-bunched oscillation of FEL, it is required to increase the bunch charge up to 50 pC for the t-ACTS accelerator. However, the maximum bunch charge of the current thermionic RF gun is limited to about 5 pC due to the back-bombardment effect. To overcome this limitation, a project is underway to replace the current thermionic cathode for the RF gun with a photocathode. Currently, the laser system for the photo-injector is being constructed. The system consists of a Yb fiber laser oscillator with a synchronization system, a pulse extraction section, an amplifier stage, and a wavelength conversion section. The project aims to produce a UV laser with an energy of more than 2 µJ and to achieve a phase difference between the laser system and the RF system of less than 1 degree with respect to a frequency of 2856 MHz. We will present the status of the laser system in terms of the improvements of the laser power and the synchronization for the upcoming photo-injector in t-ACTS.