The zero helicity and chirality of optical vortices

We show that any uniformly linearly-polarised paraxial vortex mode carrying orbital angular momentum (OAM) has zero spin (SAM) density, but exhibits non-zero helicity density distributions. Such a then possesses chirality as confirmed by experiment and so can engage with chiral matter. confining the treatment for general fields only to leading order leads directly agreement of our theory experimental results, provided we ensure crucially obey duality. find space integral densities vanish identically all such optical modes without specifying kind mode. These generally applicable properties thus assert due elliptical wave polarisation index ?, an alone cannot possess total helicity, even though it always