Interaction of Bessel optical vortices in quadratic nonlinear medium

A vortical structure of second harmonic (SH) field excited in quadratic non linear medium by combined beam composed of two multiple-charged Bessel vort ices of fundamental frequency (FF) is analyzed. An emergence of the pairs o f single-charged vortices in SH beam caused by interaction of Bessel vortic es is revealed. The charges of the vortices in these pairs can be the same (both positive), as well as different. We show, that in spite of any variat ion in the number of vortices in SH beam, the doubling of total topological charge of FF beam takes place in SH generation process. The derived result s correspond to the negligible pump depletion in the case of exact noncriti cal phase matching and neglect of SH beam diffraction. (C) 2001 Elsevier Sc ience B.V. All rights reserved.