Generation of Terahertz Coherent Synchrotron Radiation by using Laser and Electron Beam

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We have succeeded in producing coherent synchrotron radiation in the terahertz region by using relativistic electron bunches with micro-density structures. The micro-structures were created by a newly developed method, which utilize the interaction between electrons and laser field. Electrons traveling with laser pulse in alternating magnetic field can exchange their energy with laser field under some resonant condition. As the result, an energy modulation is created on the electron bunch. This energy modulation is converted to a density modulation as the electron bunch is proceeding in the accelerator, as the result of the energy dependence of the path length. Such system has been constructed on the UVSOR-II electron storage ring in Institute for Molecular Science.We have successfully demonstrated that an electron bunch with a single dip structure of sub-picosecond width emitted intense broadband coherent THz pulse. The dip structure was created by injecting femtosecond laser pulses into the storage ring.We have also demonstrated that an electron bunch with a periodic micro-structure of a sub-picosecond period emitted narrowband coherent THz pulse. In this case, amplitude modulated laser pulses are injected into the ring, which were created by newly developed system in collaboration with a research group of Lille University France. It is well known that synchrotron radiation is extremely broadband from radio-wave to X-rays. This is the first experimental result that monochromatic synchrotron radiation is extracted from a uniform magnetic field. By changing the period of the microstructure, we could change the radiation wavelength.The results have indicated the possibility to control the amplitude and the phase of synchrotron radiation. The developed method can be realized most of the existing synchrotron light sources.