On focusing of laser radiation with an axicon

The influence of axially symmetric perturbations of the intensity and phase of the laser beam on its focusing by means of an axicon is considered. It is shown that such perturbations give rise to variations in the radiation energy density on the axicon axis with two periods, Λ/γ and Λ²/λ, where λ is the period of perturbation of the laser beam intensity, and γ is the angle of convergence of the focused beam.