Measurement of coherent Cherenkov radiation from an intense beam of a picosecond electron bunch

High-intensity Cherenkov radiation (CR), emitted in air from a high-current 30-MeV electron bunch (2×${10}^{11}$ electrons/bunch) of the linear accelerator at the Institute of Scientific and Industrial Research was observed at wavelengths from 0.4 to 3 mm. The radiation was emitted at an angle of 38 mrad, with some spread, from the beam axis. The radiation measured was about ${10}^{11}$ times as intense as that calculated for ordinary CR. Such enhancement is attributed to the coherence which appears in CR emitted from electron bunches of relatively short length.