Correspondence principle in multiphoton inverse bremsstrahlung

Multiphoton electron-ion inverse bremsstrahlung is studied using the correspondence principle. It is shown that the existing quantum-mechanical theory of this phenomenon is only valid in the low-frequency limit omega tau <<1. A different approach is suggested which enables the author to obtain the multiphoton cross sections for all values of omega tau . Using these cross sections, the absorption coefficient of laser radiation in an isotropic plasma is found.