News ID: 220320
Published: 0415 GMT August 25, 2018

New light momentum measuring device illuminates 150-year-old scientific principle

New light momentum measuring device illuminates 150-year-old scientific principle

Light Momentum theory is receiving renewed interest in the scientific community thanks to a fresh approach involving radiation pressure. Who says you can't teach an old dog new tricks?

There are some central scientific theories and frameworks which remain dormant for years after they are established, like a classic novel that collects dust on the shelf of a large bookcase. What's needed, most often, is for the right individual, or group, of scientists to revisit the concept and apply methods that will breathe new life into old ideas, wrote.

One example is a study carried out by an international research team that is now opening up the conversation about light momentum, specifically the details about light and matter interaction. It was close to a century-and-a-half ago, in the 1870s, that James Clerk Maxwell put forth his theory that the momentum held within electromagnetic fields is responsible for radiation pressure.

Since that time, it has been generally accepted in the scientific community that a process, known as momentum conversion, occurs when electromagnetic fields become elastic waves as they pass through elastodynamic and electrodynamic phenomena.

What was missing, however, was a complete understanding of how this intricate process of photo interaction occurs. To make the picture clearer, the research team used a fresh approach which involved a special dielectric mirror equipped with heat shields and sound sensors.

By using radiation pressure, laser pulses were passed along the surface of the mirror as the sensors detected the elastic waves as they traveled. This setup allowed the researchers to make some attempts at accurately measuring this very delicate process.

Previous experiments applying radiation pressure had been carried out by some of the same scientists in recent years, but the results were incomplete because of the equipment involved. University of British Columbia Associate Professor in Engineering Kenneth Chau, who was involved in this study and previous studies, stated that the research is the beginning of a larger conversation about light momentum, and should in no way be seen as a definitive landmark study:

“Until now, we hadn’t determined how this momentum is converted into force or movement,” he said. “Because the amount of momentum carried by light is very small, we haven’t had equipment sensitive enough to solve this. We were able to trace the features of those [elastic] 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.”

Radiation pressure offers a wealth of additional benefits that go beyond the area of scientific research. Professor Chau also pointed out that he is motivated by the potential real-world applications of the novel method:

“Imagine traveling to distant stars on interstellar yachts powered by solar sails. Or perhaps, here on Earth, developing optical tweezers that could assemble microscopic machines. We’re not there yet, but the discovery in this work is an important step and I’m excited to see where it takes us next.”

Details about the study can be found in an article, titled "Isolated detection of elastic waves driven by the momentum of light", which was published this week in the Nature Communications journal.


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