The image you see just above looks a lot like a satellite image of a large river delta, where the main channel begins to split into smaller channels and channels, which in turn split into even smaller ones. Something similar can occur when waves propagate in a certain environment, this phenomenon is called "branching flow" and it has already been observed by physicists in relation to electron flows (electric current), sound waves and ocean waves.
Now, scientists have succeeded in achieving this phenomenon in relation to visible light, and it turned out to be quite simple to do this, because all that was required for this was a laser and a foam consisting of small soap bubbles.
A branching flow requires an environment with certain properties. Its structure should be random, the elements that make up the structure of the medium should be greater than the wavelength of the flow. And changes in the structure of the environment should occur quite smoothly, without any abrupt transitions. If all these conditions are met, small changes and fluctuations in the structure of the medium can dissipate the flow, causing it to separate and constantly “branch”.
The branching flow behavior is typical for waves having a sufficiently long length, but obtaining such a phenomenon in relation to waves of light was quite difficult until researchers from the Technion Institute of Technology and the University of Central Florida came up with the use of foam from soap bubbles as a medium for the propagation of light …
The membrane of each bubble consists of a very thin layer of liquid sandwiched between two layers of surfactant molecules. The thickness of all this varies from five nanometers to several nanometers and such differences in thickness produce the well-known colorful images on the surface of soap bubbles. But, these same differences in thickness can act as a kind of mirrors that cause a stream of light passing through them to refract, split and branch.
By directing a beam of laser light, which was previously given a special "flat" shape, through the soap suds, the scientists saw that this beam began to spread along the trajectory of a branching stream. Later, replacing a fairly bright laser light with a beam of weak white light, scientists watched as this beam began to change color, splitting into smaller beams. In ordinary soap bubbles, the air flow around the membrane causes constant changes in its thickness, which leads to the fact that the color images on the surface are constantly changing shape and moving. There are no significant air currents in the lather, and the split light images can remain stable for several minutes.
Note that this achievement can have a very strong impact on the field of so-called opto-fluidics, a field of science devoted to the interaction of light with different liquids. And, if you give free rein to your imagination, then you can imagine a certain optical processor that performs calculations, manipulating the streams of light with the help of artificially created differences in the thickness of the membranes in the medium through which this light passes.
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And in conclusion, it should be mentioned that the branching of the light flux in three dimensions is a phenomenon, the possibility of which scientists have guessed for quite a long time, but which has never been observed in practice until recently.
