Tying light into knots

Scientists can tie light into knots. And those knots can stabilize nuclear fusion. Because every day, physics gets crazier.

Over the last few thousand years, light has moved from a mystical expression of divine power, to a comprehensible phenomenon, to another piece of lab equipment. 'Optical tweezers' or 'optical traps' are often used in laboratories to do delicate work. But how do you tie a knot in a beam of light? First, you have to bend it.

Optical tweezers let scientists use light to manipulate matter by focusing a low-intensity laser beam on an object. If the object moves, it diverts the course of the laser beam, the way moving a hand in front of a garden hose pushes the water one way or another. Anyone who has put a hand in front of a hose knows that when they divert the water one way, their hand feels a push in the opposite direction. The object feels the same push whenever it moves out of position. If the object moves to the left, the light is diverted to the left, and the object gets a push to the right - and moves back into position.

But light doesn't have to be focused to a point. It can be focused to a line, or a curve. Although it's not an intuitive phenomenon, most people have seen curves of intense light crawling across the bottom of a swimming pool, or behind a lit-up piece of cut glass. These patterns are two-dimensional, running along a flat surface, but if they are projected as a hologram, they can be three dimensional. A three-dimensional band of light can curve up, over, and back in on itself, creating an optical knot. This can channel material along its curve, and trap it.

There are a few possible applications for this technology, but one of the most exciting of them is in nuclear fusion. Fusion works by heating atoms until they slam into each other hard enough to stick together. The resulting combo-atom loses a little mass as energy. That energy can be used to produce electric power. Fusion requires high temperatures, and one way those temperatures can be reached is the application of electromagnetic current. The problem is, the plasma created in the fusion materials by these temperatures tends to make the current hard to control. It heats the material unpredictably, damaging the plasma container and sometimes even cooling the plasma down. If the electromagnetic current could be tied up in a knot, looping back in on itself over and over, it would be contained. It would boost energy production while making the production safer.

Via NYU, Zeitnews, Universe Today, OSA, Science Codex, and Medical News Today.