Radiation from Nonlinearly Excited Plasmas

Longitudinal plasma oscillations can be excited nonlinearly by two strong incident electromagnetic waves. The reradiation from such nonlinearly excited plasma is calculated for the cases of a thin plasma film and a small plasma column. Finite-temperature effects are neglected, but the dominant mechanism of coupling between longitudinal and transverse waves by boundaries is properly taken into account. Resonances in such reradiation from both the thin film and the small column are found at frequencies ${\omega }_p$ and $\frac{{\omega }_p}{\sqrt{2}}$, respectively, where ${\omega }_p$ is the plasma frequency. The intensity of such reradiation is compared with the scattered intensity of another electromagnetic wave from the same nonlinearly excited plasma. It is found quite generally that the reradiation dominates the scattering, thereby explaining the result of a recent experiment.