Spatial soliton-induced cloning, which achieves and maintains perfect spatial overlap of interacting beams, is proposed as a tool for amplification of nonlinear optical effects on propagation. This is illustrated by the enhancement of the parametric amplification, obtained through pump-induced cloning of the transverse profiles of the copropagating probe and generated four-wave mixing beams, in an all-optical antiwaveguiding configuration.Spatial soliton-induced cloning, which achieves and maintains perfect, spatial overlap of interacting light beams, is proposed as an alternative method for strong enhancement of nonlinear optical effects on propagation. The specific conditions under which this method can be implemented will be analyzed for a particular case. We consider the enhancement of parametric amplification ͑PA͒ resulting from the pumpinduced cloning of the transverse profiles of a weak probe, and of the generated four-wave mixing ͑FWM͒ beam, for the case where the pump has a doughnut-shaped transverse profile ͓1͔. The waist size of the Gaussian transverse profile of the input probe beam is chosen to be much smaller than that of the Laguerre-Gaussian pump so that, initially, there is no overlap of the beams. The beams propagate coaxially in a medium of two-level atoms. Due to self-focusing and diffraction, the pump beam is transformed into a bright vortex, or doughnut, spatial soliton ͓2͔. Cloning arises from diffraction and sufficiently strong pump-induced focusing ͓3͔ of the probe and of the generated FWM beam, and leads to enhanced PA of both beams on propagation. We have verified that in an alternative scenario, where the pump-induced focusing of the probe is weaker, the probe intensity still leaves the region of the propagation axis and concentrates in the bright region of the pump. However, the overlap between the pump and probe beams is less perfect, leading at first to weak PA. On further propagation, PA increases the probe and FWM intensity and this eventually leads to cloning since PA is controlled by the pump. Thus PA seems to reinforce the effect of cross-focusing ͓4͔ and reduces the anticloning tendency of diffraction, thereby playing a self-referential role.Amplification depends on the propagation distance and therefore transverse instability, leading to breakup of the bright vortex soliton, must be suppressed. This is achieved by working under saturation conditions ͓2͔ and using computer-generated holograms rather than a cylindrical lens mode converter to prepare the Laguerre-Gaussian beam ͓1,5͔. In this way, one can avoid azimuthal-symmetrybreaking perturbations that introduce ellipticity into the transverse profile ͓2͔. In computer simulations, azimuthal symmetry breaking is avoided by using a polar grid that prevents the numerical noise effects of discretizing a ring onto a rectangular grid ͓2͔. Thus the transverse field keeps its initial azimuthal symmetry so that a cylindrical twodimensional numerical method can be used to calculate the beam propagation ͓6͔.Cloning has been discussed by...
