Beam cleanup with stimulated Raman scattering in the intensity-averaging regime

We describe experimental and theoretical investigations of beam cleanup with highly aberrated pump beams in the intensity-averaging regime. Distortion-free amplification of a diffraction-limited Stokes beam is demonstrated in a crossed-beam geometry with a pump beam aberrated to 120 times its diffraction limit, resulting in a brightness increase of 5000 times. Moderately aberrated pump beams produce off-axis Stokes components, while collinear interactions introduce distortion on the Stokes beam. Phase conjugation is combined with stimulated Raman scattering to remove both the aberrations of the pump beam and the aberrations on the Stokes beam itself.