Researchers Discover a New Property of Light

You might think that physicists have a complete understanding of the properties of light, but that turns out not to be true. A team of researchers at the University of Salamanca have discovered a new property of light, called self-torque. 

First, let's take a step back. Over the last few decades, physicists have discovered that it is possible to twist the wavefront of a light beam, giving it angular momentum. This looks a bit like a spiral staircase, with the beam wrapping around an empty middle. When such a beam is targeted at something, you see a bright donut. These beams are said to have orbital angular momentum (OAM), a property not dependent on polarization (which instead is about the geometry of the electromagnetic oscillations.)

As reported in the latest issue of the journal Science, researchers have discovered that it's possible for an OAM light beam to exhibit "self-torque". As the beam moves forward, its twist goes from wider to narrower, a bit like a screw. If such a beam is projected onto a flat surface, it would appear in the shape of a croissant or crescent.

At this point, it's not clear if there is any practical use for the phenomenon, but science is like that. Give it time, and someone will think of  something.

Do watch the video, by the way. It shows the complexity the equipment used in modern physical research. It's way beyond anything in the labs when I was studying physics in university.