Abstract
Coupled-mode equations for the nonresonant interaction of two high-frequency surface waves, propagating along a plasma column bounded by vacuum, are derived directly by solving the equations of the one-fluid cold collisionless/collisional plasma model. The coupling coefficients are obtained in explicit form. The results are verified by analysing the simple case of harmonic generation by a high amplitude wave. The theory is extended to three-wave interaction in loss plasma in the general case of imperfect synchronism.