New Form of Light Discovered

                Scientists have discovered a new form of light, which will impact our understanding of the fundamental nature of light. One of the measurable characteristics of a beam of light is known as angular momentum. Until now, it was thought that in all forms of light the angular momentum would be a multiple of Planck’s constant – the physical constant that sets the scale of quantum effects.

                Now, researchers have demonstrated a new form of light where the angular momentum of each photon (a particle of visible light) takes only half of this value. This difference though small is profound, researchers said. “We’re interested in finding out how we can change the way light behaves, and how that could be useful. What we think is so exciting about this result is that even this fundamental property of light, that physicists have always thought was fixed, can be changed,” researchers said.

                This discovery will have real impact for the study of light waves in areas such as secure optical communications. In the 1830’s, the mathematician William Rowan Hamilton and physicist Humphrey Lloyd found that, upon passing through certain crystals, a ray of light became a hollow cylinder. The team used this phenomenon to generate beams of light with a screw-like structure.

                Analyzing these beams within the theory of quantum mechanics they predicted that the angular momentum of the photon would be half-integer, and devised and experiment to test their prediction. Using a specially constructed device they were able to measure the flow of angular momentum in a beam of light. They were also able, for the first time, to measure the variations in this flow caused by quantum effects. The experiments showed a tiny shift, one half of Planck’s constant, in the angular momentum of each photon.