Parametric down-conversion of Bessel vortex beam in quadratic medium

This study predicts and demonstrates that orbital angular momentum (OAM) is conserved within the spontaneous down-conversion of Bessel vortex beam in optical parametric generators (OPG). Results show that the output radiation of CDA-based OPG pumped by Bessel vortex beam consists of two pairs of OAM-free axial (Gaussian-like) beam and the conical (Bessel-like) beam, the OAM of which is equal to OAM of pump beam. Hence, the OAM is conserved within the spontaneous parametric down-conversion of higher-order Bessel beams in contrary to OPG pumped by Laguerre-Gaussian modes. That is the result of strong transverse selection of spontaneously arising fields in OPG pumped by Bessel beams.