To understand the pulse of light: scientists found the solution to a 150 year old riddle

The idea that light has momentum, not new, but the exact nature of how light interacts with matter remained a mystery for almost 150 years. A new study recently published in Nature Communications, may have discovered the key to one of the darkest secrets of the world.

Johannes Kepler, the famous German astronomer and mathematician, was first suggested in 1619 that the pressure of sunlight may be the reason that the comet tail always point away from the Sun, said study co-author and Professor of engineering at UBC Okanagan, Kenneth Chow. Only in 1873, James Clerk Maxwell predicted it radiatsionnoe pressure is related to the impulse that is within the electromagnetic fields of the light itself.

“So far we have not determined how the momentum is converted into force or movement,” says Chow. “As the momentum carried by light is very small, we have not been sensitive enough to identify equipment”.

Now technology has appeared and Chow, with his international research team from Slovenia and Brazil, sheds light on this mystery.

To measure these extremely weak interaction between the photons of light, the team has built a special mirror, equipped with acoustic sensors and thermal protection, to reduce interference and background noise to a minimum. They then fired laser pulses into the mirror and used sound sensors to detect elastic waves on the surface of the mirror, like ripples on a pond.

Momentum of light: how to find?

“We cannot directly measure the momentum of photons, so our approach was to detect its influence on the mirror, “listening to” the waves that passed through it,” says Chou. “We were able to trace the features of these waves to the pulse that is the pulse of light that finally opens the door for simulations of light pulse in materials.”

This discovery is important for understanding the world, but Chow also notes a possible practical application of light pressure, for example in solar sails.

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