Observation of interference between coherent synchrotron radiation from periodic bunches

An interferogram of synchrotron radiation emitted from a train of bunched electrons accelerated by an S-band linac has been observed in the far-infrared region using a polarizing interferometer whose maximum optical path difference covers a distance between adjacent bunches. The interferogram shows that radiation emitted from successive bunches is coherent, and that coherent synchrotron radiation emitted from periodic bunches has a spectrum of a line series, i.e., higher harmonics of the radio frequency of the linac.