The creation and annihilation of optical vortices using cascade conical diffraction

Internal conical diffraction produces a superposition of orthogonally polarised zero- and first-order Bessel like beams from an incident circularly polarised Gaussian beam. For right-circularly polarised light, the first-order beam has an optical vortex of charge −1. Upon propagation of the first-order beam through a second biaxial crystal, a process which is termed cascade conical refraction, the generated beam is a superposition of orthogonally polarised fields of charge 0 and −1 or 0 and −2. This spin to orbital angular momentum conversion provides a new method for the generation and annihilation of optical vortices in an all-optical arrangement that is solely dependent on the incident polarisation and vortex handedness.
We acknowledge the support of Science Foundation Ireland under research grants 06/RFP/PHY029, SFI/SIRG/I1592 and 08/IN.1/I1862 and Sir Michael Berry for helpful discussions.