Multiphotone processes and nonlinear effects of electromagnetic wave propagation in a plasma

On the basis of S matrix theory for free-free transitions in presentation of coherent states calculated are the effective frequency of Coulomb collisions of particles and permittivity of a plasma in strong electromagnetic wave field. It is shown that the abnormal wave penetration into the plasma at frequencies less than the Langmuir frequency takes place. This fact facilitates the irradiation diffusion into the Coulomb system. It is underlined that this conclusion can be important when choosing conditions of operation for laser thermonuclear generator