Breakup of beams with a regular spatial structure in a cubic medium

Experimental and theoretical studies were made of the characteristics of an instability of beams with regular spatial spectra in the presence of small-scale self-focusing. The process differed qualitatively from small-scale self-focusing of a plane wave and the difference was due to the possibility of simultaneous growth of perturbations, of various spatial spectral components in the field of several pump components in the case of spatial phase matching between the interacting waves. The growth increments of the instabilities were calculated for different types of spatial spectra of pump beams.