Experimental observation of the small-scale self-focusing of a beam in the nondestructive regime

Two methods for the experimental study of the nonlinear interaction of the fundamental beam and noise component of high-power laser radiation under conditions of small-scale self-focusing in the nondestructive regime are proposed and realised. In the case of the nonlinear phase shift B = 1, the theoretically predicted circular structure of the spatial spectra of the field and laser beam intensity (pulse energy 20 J and peak power 20 GW) propagated through a glass sample was experimentally observed.