a method for eliminating small - scale , spatial intensity fluctuations in laser beams is disclosed comprising the steps of placing in the path of the laser beam at least one nonlinear filtering element constituted by a fluid medium , having an index of refraction increasing with the intensity of light passing through the fluid medium and focusing only the laser &# 39 ; s small - scale , spatial intensity fluctuations above a predetermined power threshold at a focal point within the fluid medium whereby the energy contained in these fluctuations is dissipated . alternatively , the nonlinear filter element can be constituted by a fluid medium wherein high - frequency sound waves propagate with low attenuation wherein only the small - scale , spatial intensity fluctuations above a stimulated brillouin power threshold are back - reflected whereby the energy contained in those fluctuations is eliminated .