Čerenkov radiation from a finite-length path in a gas

Abstract

Measurements of microwave \ifmmode \check{C}\else \v{C}\fi{}erenkov radiation in air show that the \ifmmode \check{C}\else \v{C}\fi{}erenkov cone angle is broadened as predicted in earlier work. Extension of previous theory shows that for small \ifmmode \check{C}\else \v{C}\fi{}erenkov angles, the broadening is asymmetric, giving an increase in the effective cone angle to a value in agreement with the experimental results. The shift in the radiation peak can be understood as a diffraction effect arising from the linearly varying phase of the radiation along the beam interaction length.