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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 (2x 10 n 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 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.