Induced focusing of optical beams in self-defocusing nonlinear media

The novel phenomenon of induced focusing occurring in a self-defocusing nonlinear medium is discussed theoretically. Induced focusing of a weak optical beam occurs when it copropagates with an intense pump beam whose intensity peaks at a place different from that of the weak beam. The physical mechanism behind induced focusing is cross-phase modulation that couples the two beams. The conditions under which induced focusing can occur are discussed by solving numerically the coupled amplitude equations which incorporate the effects of diffraction, self-phase modulation, and cross-phase modulation.