Interaction of spatial solitons in nonlinear optical medium
  The effects caused by nonresonant nonlinear interaction between noncollinear self-focusing beams are considered in 2D optical samples using multi-scale analysis. The analytical expression for the beams trajectories shift due to the mutual interaction is derived, and the range of parameters is given beyond which the mentioned consideration fails. We compare our results with the naive geometrical optics model. It is shown that these two approaches give the same results. This justifies the use of geometrical optics approach for description of elastic and almost-elastic collision processes both in Kerr and saturable nonlinear media. 
Ramaz Khomeriki, Lasha Tkeshelashvili