New Form of Light

Planck’s constant is a fundamental physical constant that relates the energy of a single photon of light to the frequency of its wave. It has long been thought that all light possessed an angular momentum (the degree to which a beam of light rotates around its own axis) that is a multiple of this constant. But a new form of light has been discovered in which the angular momentum is only half that value — a breakthrough that could have a profound impact on the study of light for applications like secure optical communication.

In the 1830s, at the same institution, researchers had discovered that when a ray of light passed through certain crystals, it became a hollow cylinder. The current researchers used this phenomenon to generate screw-like beams of light. Using a special device, they were able to measure variations in the flow of angular momentum of the beam caused by quantum effects, revealing a shift in each photon equal to one-half of Planck’s constant.

This discovery challenges our understanding of some of the most basic principles of physics, and illustrates once again that the more we learn, the more we realize just how little we know!

For information: Stefano Sanvito, Trinity College Dublin, Centre for Research on Adaptive Nanostructures & Nanodevices, College Green, Dublin 2, Ireland; phone: +353-1-986-1000; email: Stefano.sanvito@tcd.ie; website: http://crann.tcd.ie/Home.aspx