Abstract
Beam cleanup1 and beam combining2 depend strongly on the geometry of the interaction volume of the Raman amplifier. During the propagation of the TEM00 Stokes seed, the amplification by the multimode pump beam generates many additional high order modes. However, due to the propagation through the interaction region, these higher modes are filtered away since only the modes that fall within the solid angle determined by the geometry are amplified. Therefore, focused beams are investigated in order to have a geometry with a low Fresnel number.