Theory of lossless suppression of filamentation in high-power laser beams

Abstract

This paper supports an earlier suggestion that saturation of the optical nonlinearity of a medium by a plane wave will suppress filamentation of the wave. A variational approach and exact solutions of the slowly-varying-envelope approximation of the linearized wave equation describe the growth of localized filaments on plane waves. The solutions show that a wave will be stable against filamentation if the wave is weak or if it is intense enough to saturate the nonlinearity of the medium. Experiments are proposed to demonstrate suppression of filamentation of CO2 laser beams exceeding 1010 W and Nd laser beams exceeding 1012 W in fully ionized hydrogen plasmas. The beams saturate the nonlinearity of the plasma by ponderomotive forces; absorption is negligible in the rarefied channel produced by the laser. Applications may include lossless filters that remove intensity hot spots from beams or convert mulitmode beams to nearly single mode.