Non-linear generation of combination frequencies in a plasma

In this paper the authors have considered the generation of combination frequencies due to two strong uniform parallel electric fields of frequencies ω 1 and ω 2 in a homogeneous plasma; it is found necessary to introduce terms containing exp { i (ω 1 ± ω 2 ) t } in f o (the symmetrical part of the distribution function f ) and f 2 (the higher-order asymmetrical part appearing as the third term in a Legendre polynomial expansion of f ), because their contributions to the combination frequency components of current density are appreciable. The growth of the combination frequency waves in a plasma and their appearance in the reflected waves from a plasma-free-space interface when two electromagnetic waves of frequencies ω 1 and ω 2 are propagating along the same direction (normal to the interface) has also been studied. Some numerical results have been presented in the discussion at the end.