Sum-frequency excitation of electron plasma waves

Nonlinear mixing of two circularly polarized electromagnetic waves propagating in a plasma along a uniform static magnetic field is considered. Resonant excitation of electron plasma waves is found to be possible at the difference frequency if the incident waves are both extraordinary or both ordinary and at the sum frequency if one incident wave is extraordinary and the other is ordinary. Formulas for the absorption efficiency due to sum-frequency excitation are derived and the results of a numerical study are presented.