Diffraction catastrophe in the focusing region of an aberrated laser beam and associated optical vortices

A structurally stable caustic formation, comprising a so-called diffraction catastrophe, is formed in the region of the focus of a convergent laser be am distorted by spherical aberration and astigmatism. The amplitude and pha se distributions of the field in the region of the diffraction catastrophe are calculated. Screw dislocations of the phase are detected in the diffrac tion field under consideration, forming complex loops in three-dimensional space and constituting the axes of the corresponding optical vortices. From the large collection of screw dislocations, we can distinguish closed, com pactly localized dislocations. The latter are located in "dark" regions ins ide the caustic and separate one cell (elongated in the z direction) with h igh field intensity from another in a geometrically correct way. (C) 1999 T he Optical Society of America. [S 1070-9762(99)0081 2-X].