Super-critical phasematching for photon pair generation in structured light modes

TL;DR

This paper introduces a novel super-critical phasematching technique for generating radially and azimuthally polarized photon pairs via SPDC using a Bessel-Gauss pump beam aligned with the crystal axis, enabling control through the pump's opening angle.

Contribution

It presents a new geometry for SPDC called super-critical phasematching, allowing direct control of polarization and spatial properties of photon pairs without tuning the crystal axis.

Findings

Modelled spatial and polarization output distributions for Type-I and Type-II configurations.

Demonstrated control of phasematching conditions via pump beam opening angle.

Proposed a practical method for generating structured light photon pairs.

Abstract

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.