Control of the formation of vortex Bessel beams in uniaxial crystals by varying the beam divergence

The transformation of zero-order Bessel beams into a second-order vortex Bessel beam in CaCO₃ and LiNbO₃ crystals is experimentally studied, and a possibility of controlling the beam transformation by changing the wavefront curvature of the illuminating beam is shown. A quasi-periodic nature of the Bessel beam transformation in a crystal while illuminating the diffraction axicon by a convergent beam is observed.