The Dark Side of Light
February 19, 2008 By Lisa Zyga
The model of vortex structure in laser speckle. Open vortex lines are in red, while closed vortex loops are in white. Credit: O’Holleran, et al.
Light may not seem very interesting in our everyday lives. But to scientists, light’s properties are a constant source of intrigue. The nature of light as both wave and particle, light as the universal speed limit, and the way light interacts with magnetic fields in the atmosphere to form auroras are a just a few examples of light’s fascinating behavior.
Recently, researchers from the University of Glasgow and the University of Bristol in the UK have discovered another unusual property of light – or, more accurately, the darkness within light. As the researchers explain, natural light fields are threaded by lines of darkness, which create optical vortices that appear as black points within the light. The group has modeled this phenomenon, and found that the lines of darkness exhibit fractal properties with Brownian (random) characteristics. Further, the characteristics of these optical vortices suggest universal properties, which could help connect different areas of physics.
Many people have noticed the phenomenon of laser speckle, which occurs when coherent, monochromatic laser light bounces off a rough surface, giving the surface a speckled appearance. The black specks are interference patterns generated by a superposition of highly coherent light waves reflected from different points on the rough surface. Sometimes the speckled pattern can even appear to sparkle when the viewer moves relative to the surface.
In a recent issue of Physical Review Letters, the UK researchers describe how they developed a model of the superpositions that create the dark optical vortices, using numerical simulations and experiments. In their experiments, they created laser speckle with a 10-mm-diameter helium neon laser beam shining through a screen made of ground glass.
By measuring the superpositions with an interferometer, the scientists could generate a 3D map of the structure of the optical vortices. They found two types of vortices. Infinite vortex lines, which account for about 73% of the dark vortices, percolate entirely through the light beam. The remaining 27% of the vortices form closed loops, which occur when a vortex line returns to its starting point within a small enough area.
When investigating the lines of darkness further, the researchers found that they exhibit scale invariance. In other words, the vortices look the same no matter how much you zoom out – they are fractals. Lead author Kevin O’Holleran of the University of Glasgow said that, while he and his colleagues suspected vortex lines to exhibit fractal properties, they were quite surprised to find that the fractality was of a Brownian nature.
“To find that the vortex lines in light have Brownian characteristics is exciting,” O’Holleran told PhysOrg.com. “Brownian structures are inherently random, so the coherence of our model was in no way limiting the fractal behavior of the vortex lines. We are looking forward to exploring these properties in more detail. More specifically, we hope to investigate the topological side of random light fields, such as how often vortex lines are knotted or linked.”
Interestingly, the researchers noted that these properties of optical vortices (the ratio of vortex lines to loops and their scale invariance) are very similar to the properties of cosmic strings, according to the cosmic string lattice model. The model describes the configuration of cosmic strings in the early universe – the very thin but very dense one-dimensional defects in space-time that could be responsible for the formation of galaxies.
The researchers don’t think this similarity is likely to be coincidental. They suggest that these properties could be universal for all optical fields, and they plan to investigate the analogy further.
“The greatest significance [of this study] is the connection to other fields in physics,” O’Holleran said. “Universal properties connect fields of research at deeper levels than the exact formulation of each system. Shared fundamental properties or restrictions (like how lines can be embedded in 3D space) result in universal exponents appearing in varied and apparently disconnected fields of research. The fact that vortex lines in light exhibit power laws suggesting universal properties means that these lines are governed by more general laws than wave equations.”
More information: O’Holleran, Kevin, Dennis, Mark R., Flossmann, Florian, and Padgett, Miles J. “Fractality of Light’s Darkness.” Physical Review Letters 100, 053902 (2008).
Copyright 2008 PhysOrg.com.
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Oct 24, 2009 |
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"closed vortex loops are in black" You mean white?
"Vortices," oh my... And I like how it pulls in Knot theory as well.
I look forward to any follows up & developments from their research. Especially a description of the "power laws suggesting universal properties."
Just an interesting observation..
But, why the heck would a mathematical entity be concerned with the moral laws of moses anyhow!? Wouldn't a mathematical entity address the important issues like curing aids or cancer, or world hunger which also all happen to follow a fractal pattern? Hasn't, in a sense, his design failed due to inefficiencies and imperfections in the creation process!?
I think that he is more of a historo-mythical figure than a supreme deity, like Zeus and Oden.
moebiex - Indeed!
In addition to these two examples, it would be interesting to find out just how many phenomenon follow this ratio and what decides the ratio.
How many times did they repeat the experiment? For example, after every "simulation" was the ratio at or close to 27% & 73%?
They mentioned that the "lines of darkness exhibit fractal properties" ... Is this true for the lines of... lightness as well?
Again, quite a revelation.
rAmen!
And, then, by your own argument, Who/What created God?
Your argument is infinitely recursive.
While avoiding such by way of exiting the loop at an arbitrary interation named "God" may be emotionally satisfying to you, for those of us who prefer a logically consistent one it fails miserably.
Best stick to Faith, as you fail at Science.
this phenomenon may be explained by the reverse swing in the cricket during which the ball holds bit, this may create a darkness, other phenomenon may top spin. This what I understand from these.
when it grazes the materials, the spinning angle may be changing all the other physical phenomenon can be explained.
We are now seeing what seems to be scale-invariance in this structure, or the simulation anyway. This brings to mind the recent theoretical research into 'unparticles', structures that are, like this simulation, scale-invariant.
And since the percentage of vortices correlate in a close manner to the percentage of known matter in the universe, well, we have some interesting science on our hands.
I think the part of this sentence that might be most important is, "within a small enough area".
Possibly meaning this was a limitation set by the people doing the experiment and possibly rendering any coincidences of % in the occurrence of loops moot.
Just food for thought.
Wherever did you get the notion that wavelength is a function of the orientation of spin axis?