Physicists at the Technion-Israel Institute of Technology and the University of Central Florida have experimentally observed optical branching flow in liquid soap films.
The branched flow pattern is shown at the top of the interference color pattern generated by weak white light, allowing the potential landscape to be observed along with the branched flow. Image credit: Patsyk et al, doi: 10.1038 / s41586-020-2376-8.
Waves propagating through a weak messy potential with a correlation length greater than the wavelength produce surprisingly long narrow strands or branches.
Rather than producing completely random spot patterns, the slowly varying messy potential gives rise to focused filaments that divide to form a pattern that resembles tree branches.
This phenomenon is called branched flow. It was first observed for electrons and for microwave cavities and is generally expected for waves with very different wavelengths.
“We are familiar with the fact that waves propagate when they propagate in a homogeneous medium. But for other types of media, waves can behave in very different ways, “said co-author lead professor Miguel Bandres, a researcher at the University of Central Florida College of Optics and Photonics.
“When we have a messy environment where the variations are smooth, like a landscape of mountains and valleys, the waves will spread in a peculiar way.”
“They will form channels that keep dividing as the wave spreads, forming a beautiful pattern that resembles the branches of a tree.”
In the study, Professor Bandres and his colleagues attached a laser beam to a soap membrane, which contains random variations in the thickness of the membrane.
They found that when light spreads within the soap film, instead of scattering, the light forms elongated branches, creating the branched flow phenomenon for light.
“In optics, we usually work hard to keep the light in focus and spread like a collimated beam, but here the surprise is that the random structure of the soap film naturally caused the light to stay in focus. It’s another of nature’s surprises, “said first author Anatoly Patsyk, a Ph.D. student at the Department of Physics and the Solid State Institute at the Technion-Israel Institute of Technology.
“There is nothing more exciting than discovering something new and this is the first demonstration of this phenomenon with light waves,” added co-author Professor Uri Sivan of the Department of Physics and Solid State Institute and the Russell Berrie Institute of Nanotechnology. at Technion. Israel Institute of Technology.
“This shows that intriguing phenomena can also be observed in simple systems and one only has to be perceptive enough to discover them. As such, bringing together and combining the opinions of researchers from different backgrounds and disciplines has produced some really interesting ideas. “
“The fact that we observe it with light waves opens up remarkable new possibilities for research, starting with the fact that we can characterize the medium in which light propagates with very high precision and the fact that we can also follow those branches accurately and study their properties. “
“Now with this observation we can think of a lot of new ideas,” said co-author Professor Mordechai Segev, also from the Department of Physics and the Solid State Institute and the Russell Berrie Institute of Nanotechnology at the Technion Institute of Technology. -Israel.
“For example, using these light branches to control the flow of fluids in the liquid, or to combine soap with fluorescent material and make the branches become small lasers.”
“Or use soap membranes as a platform to explore wave fundamentals, such as transitions from ordinary dispersion that is always diffuse, to branched flow, and subsequently to Anderson’s location.”
“There are many ways to continue this groundbreaking study. As we have done many times in the past, we would like to boldly go where no one has gone before. “
The team’s article was published in the July 1, 2020 issue of the magazine. Nature.
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A. Patsyk et al. 2020. Observation of the branched light flow. Nature 583, 60-65; doi: 10.1038 / s41586-020-2376-8
