Influence of four-wave mixing and walk-off on the self-focusing of coupledwaves

Four-wave mixing and walk-off between two optical beams are! investigated F or focusing Kerr media. It is shown that four-wave mixing reinforces the se lf-focusing of mutually trapped waves by lowering their power threshold for collapse, only when their phase mismatch is small. On the contrary, walk-o ff inhibits the collapse by detrapping the beams, whose partial centroids e xperience nonlinear oscillations.