J. Europ. Opt. Soc. Rapid Pub. 8, 13032 (2013)

Researchers at the University of Erlangen-Nuremberg, Germany have produced a novel light beam that possesses angular momentum whose axis is orthogonal to the direction of propagation. The optical state, which the researchers call a 'photonic wheel', is analogous to a bicycle wheel in motion along a path. The two types of angular momentum of light — spin momentum resulting from the light's polarization and orbital momentum produced by a twisted phase front — are usually longitudinal as their axes are parallel to the beam's motion. Peter Banzer and co-workers realize the 'photonic-wheel' state by converting a linearly polarized beam into two lateral components with opposing spin (one is left circularly polarized, whereas the other is right circularly polarized) using a special optical element consisting of two quarter waveplates. The beam is tightly focused using a microscope objective. Its electric field is then analysed by measuring the light scattered from a gold nanoparticle on a glass substrate that is scanned across the beam. The researchers propose that such a wheel state may find applications in various optical manipulation techniques, such as optical tweezers and spanners.