Chaotization and decay instability of a diffraction-catastrophe field in the presence of focusing of high-power laser radiation in a nonlinear medium

Focusing of a high-power laser beam, whose initial wave front is deformed by spherical aberration and astigmatism, in a medium with refractive-index nonlinearity is investigated by the computer experiment method. It was found that the extended formations which arise near the focus are no longer diffraction catastrophes, since they are structurally unstable. It is shown that weak disturbances of the shape of the initial wave front produce extremely strong distortions of the optical field in the focusing region. As the wave propagates in the z direction, spatial chaos in the distribution of the optical field develops in the region of focusing (from 137 to 142 mm). Optical turbulence arises in the focusing region as a result of self-diffraction of light by self-induced nonuniformities of the refractive index of the medium. After the region with the smallest cross section of the formation near the focus, the three-dimensional optical field has the form of chaotically dispersing “splashes” and extended “filamentary ejecta.” Zh. Tekh. Fiz. 68, 74–83 (September 1998)