Abstract
Radiation in the millimeter range with a broad spectrum was observed in laser plasma interaction experiments. The spectral region range of the radiation is from 26.5 to 325 GHz, which is the upper limit of the present detector, with a pulse duration of 200 ps. The direction of the radiation is symmetrical from 30 to 60° with respect to the laser direction, and its poralization is in the radial direction, i.e., the TM01 mode. This suggests that the radiation is generated by the radial oscillation of plasma electrons under the electric field of a laser generated immovable ion column. The frequency of the radiation depends on the initial electron velocity that is accelerated by the laser-generated ponderomotive force at the focal spot. To explain the angular distribution of the radiation, the radiation is emitted from the plasma column. The numerical calculation of the distribution is in good agreement with the experimental data.