LONG-WAVE INSTABILITY IN OPTICAL PARAMETRIC OSCILLATORS

We show that the full dynamical equations for optical parametric oscil lators in a large aspect ratio cavity for the case of long-wave instab ility is reduced to a Ginzburg-Landau equation near the instability th reshold. This equation enables us to introduce the concept of optical vortices in chi((2)) medium. A criterion of supercritical and subcriti cal instability is given as well as a condition of the Benjamin-Feir i nstability. (C) 1998 Elsevier Science B.V. All rights reserved.