Ultranarrow optical beams in quadratically nonlinear media

The vector Maxwell equations for the first- and second-harmonic planar beam s are solved with allowance made for the nonlinear diffraction that weakens quadratic nonlinearity. The structure of the transverse and longitudinal c omponents of the electromagnetic field of a parametric soliton is calculate d for different values of the wave vector and phase mismatch. Exact analyti c expressions are obtained for the self-similar profiles of extremally narr ow solitons, and it is shown that the width has a fundamental limit of the order of a wavelength in a linear medium. (C) 2000 MAIK "Nauka/Interperiodi ca".