Low-frequency transition radiation from a short laser pulse at the plasma boundary

The transition radiation that appears when a short laser pulse crosses the vacuum-plasma boundary and that is attributable to an vortex electric current produced at the plasma boundary by averaged ponderomotive forces has been considered for the first time. The spectral, angular, and spatiotemporal characteristics of the transition radiation in a vacuum are analyzed. It is shown that under typical conditions of present-day laser plasma experiments, the frequency of the transition radiation lies in the terahertz range and its power can reach several megawatts.