Researchers Observe Branched Light Flow for the First Time

A team of researchers at the Technion – Israel Institute of Technology have observed branched light flow for the first time. The findings are published in Nature and they appear on the cover of the July 2, 2020 issue.

The study was conducted by Ph.D. student Anatoly (Tolik) Patsyk, in collaboration with Miguel A. Bandres, who was a postdoctoral fellow at Technion when the project started and is now an assistant professor at CREOL, College of Optics and Photonics, University of Central Florida. The research was led by Technion President Professor Uri Sivan and distinguished Professor Mordechai (Moti) Segev from the Technion Schools of Physical and Electrical Engineering, the Solid State Institute and the Russell Berrie Institute of Nanotechnology.

When waves travel through landscapes that contain disturbances, they disperse naturally, often in all directions. Light scattering is a natural phenomenon found in many places in nature. For example, light scattering is the ratio of the blue color of the sky. As a result, when the length over which the disturbances vary is much greater than the wavelength, the wave disperses in an unusual way: it forms channels (branches) of greater intensity that continue to divide or branch as the wave propagates . This phenomenon is known as branched flow. It was first observed in 2001 with electrons, and it had been suggested that it was ubiquitous and that it also occurs in all waves of nature, for example sound waves and even ocean waves. Technion researchers are now bringing branching flux into the light domain: They have made an experimental observation of branching flux of light.

“We always had the intention to find something new and we were eager to find it. It wasn’t what we started looking for, but we kept looking and found something much better,” said Asst. Prof. Miguel Bandres. “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. When we have a messy medium where variations are smooth, like a landscape of mountains and valleys, the waves will spread in a peculiar way. They will form channels that will continue to divide as the wave spreads, forming a beautiful pattern that resembles the branches of a tree. “

In their research, the team 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 is another surprise of the nature, “he said. Tolik Patsyk.

The ability to create branched flux in the field of optics offers exciting new opportunities to investigate and understand this universal wave phenomenon.

“There is nothing more exciting than discovering something new and this is the first demonstration of this phenomenon with light waves,” said the president of the Technion, professor Uri Sivan, academic director of Bertoldo Badler at the Faculty of Physics. “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 led to some really interesting ideas.”

He added: “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. “

Distinguished Professor Moti Segev, Distinguished Professor Robert J. Shillman of Physics and Electrical Engineering, looks to the future. “I always educate my team to think beyond the horizon,” he said, “to think of something new and, at the same time, to look at experimental facts as they are, rather than trying to tailor experiments to meet some expected ones. Here, Tolik was trying to measure something completely different, and was surprised to see these light branches that he couldn’t initially explain. He asked Miguel to join the experiments, and together they improved the experiments considerably, to the level that they could isolate the Physics involved It was then that we began to understand what we see It was over a year before we understood that what we have is the strange phenomenon of “branched flow”, which at that time was never considered in the context of light waves. Now, with this observation, we can think of a lot of new ideas, for example, use these light branches to control the flow of fluids in the liquid, or combine soap with fluorescent material tea and make the branches turn l Little 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 project now continues in the teachers’ labs. Segev and Sivan at Technion, and in parallel in Prof. Miguel Bandres’ newly established laboratory at UCF.