Light does more than illuminate the world—it can also push and twist matter. It was back in the 1870s that James Clerk Maxwell first predicted that light carries momentum and can exert pressure on objects. Nearly a century later, in the 1970s, Arthur Ashkin asked why not use this property of light to hold and push around tiny particles. He developed optical tweezers that use focused laser beams to trap and move nanoscale objects.
While scientists have long known that light can exert small forces, detecting them has been extremely difficult. Objects at this scale are constantly jostled by random thermal motion, making the subtle influence of light hard to measure.
Now, researchers at Hokkaido University have developed a new method to measure these small forces with high precision. They then used the new technique to discover a surprising phenomenon in which light can twist tiny objects sideways, in a direction that is perpendicular to the light's direction of travel. The work is published in the journal Nature Physics.
"We developed a novel measurement platform called the 'micro-drone,' which enables, for the first time, full three-dimensional characterization of optical forces and torques acting on nanostructures," says Professor Yoshito Y. Tanaka of Hokkaido University.
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