Diffraction and order conversion of Bessel beams in uniaxial crystals

The order of a Bessel light beam propagating along the optical axes of a uniaxial crystal can be changed by two due to the influence of crystal anisotropy on beam propagation. This effect occurs because of spin-orbit coupling in crystal-traveling optical field and it is interesting for generation of high-order Bessel beams possessing optical vortices. If the input Bessel beam is apertured, the order-conversion may be distorted by diffraction spreading. A description of polarization and spatial structure evolution in crystal can be accomplished using propagation equations, which are obtained in the paper by using integral Hankel transform and solutions of Maxwell's equations for Bessel beams. The simple form of propagation equations are also derived using the Lommel functions. As an example, the order-conversion of strongly apertured zero-order Bessel beam is studied.