A photonic wheel

21.06.2013, 00:00

Newsletter 6

The angular momentum of a massive particle can be arranged to point parallel or transverse to its direction of linear motion. Longitudinal angular momentum is found, for instance, in aircraft propellers. Transverse angular momentum is present, e.g., in a spinning bicycle wheel. When considering a massless wave
system, however, the situation seems to be more restricted. Photons can carry two components of angular momentum: spin (linked to the polarization state) and orbital (related to the phase front). Both are longitudinal only (see figure, top). Thus, as far as angular momentum is concerned, light is dynamically closer to a propeller than to a bicycle wheel. We have recently demonstrated the existence of the analogue of a rolling mechanical wheel, namely a novel state of the light field with purely transverse angular momentum – a photonic wheel (see figure, bottom). We create this state by tightly focusing a spin-tailored beam and test it existence experimentally using a nanoprobing technique. A striking possibility unique to this new approach is to induce a rolling movement of a nano-object on a substrate under illumination at normal incidence. 

Contact: peter.banzer(at)mpl.mpg(dot)depeter.banzer(at)mpl.mpg(dot)de
Group: Leuchs Division
Reference: P. Banzer et al., J. Eur. Opt. Soc. Rapid Pub. 8, 13032 (2013).