Generation of short-pulse far-infrared light from electrons undergoing half-cyclotron rotation

A novel radiation source in the terahertz wave spectral region is being developed. The radiation is produced by electrons, which undergo a half-cyclotron rotation. Injecting the electron bunch with the energy of 150 MeV into the 3 m-long solenoid field, we observed that the radiation had the intense millimeter spectral component when the cyclotron resonant frequency was set to be 4 THz. The numerical calculation revealed that the radiation could be regarded as a half-cycle radiation with the pulsewidth approximately equaled to that of the electron bunch. Also, the calculation pointed out the possibility to amplify such radiation in the optical resonator.