We propose a method for directly producing radially and azimuthally polarized photon pairs through spontaneous parametric downconversion (SPDC). This method constitutes a novel geometry for SPDC, in which a radially polarized Bessel-Gauss pump beam is directed into a nonlinear crystal, with the central propagation direction parallel to the crystal axis. The phasematching conditions are controlled by changing the opening angle of the pump beam; as the crystal axis cannot be tuned, we refer to this process as super-critical phasematching. We model and plot the spatial and polarization output distributions for Type-I and Type-II super-critical phasematching.
@article{arxiv.1610.01454,
title = {Super-critical phasematching for photon pair generation in structured light modes},
author = {Rebecca Y. Saaltink and Lambert Giner and Robert W. Boyd and Ebrahim Karimi and Jeff S. Lundeen},
journal= {arXiv preprint arXiv:1610.01454},
year = {2016}
}