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The idea that light has momentum is not new, but the exact nature of how light interacts with matter has remained a mystery for close to 150 years. New research from UBC's Okanagan campus, recently published in Nature Communications, may have uncovered the key to one of the darkest secrets of light.

[...] To measure these extremely weak interactions between light photons, the team constructed a special mirror fitted with acoustic sensors and heat shielding to keep interference and background noise to a minimum. They then shot laser pulses at the mirror and used the sound sensors to detect elastic waves as they moved across the surface of the mirror, like watching ripples on a pond.

"We can't directly measure photon momentum, so our approach was to detect its effect on a mirror by 'listening' to the elastic waves that traveled through it," says [study co-author and UBC Okanagan engineering professor Kenneth] Chau. "We were able to trace the features of those waves back to the momentum residing in the light pulse itself, which opens the door to finally defining and modelling how light momentum exists inside materials."

DOI: 10.1038/s41467-018-05706-3

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