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Tapering Waveguide Captures a Rainbow
SubComdTaco passes along news of researchers in the US who have trapped a rainbow in a tapering waveguide. The research is described (PDF) on the arXiv. "In 2007, Ortwin Hess of the University of Surrey in Guildford, UK, and colleagues proposed a technique to trap light inside a tapering waveguide [made of metamaterials]... The idea is that as the waveguide tapers, the components of the light are made to stop in turn at ever narrower points. That's because any given component of the light cannot pass through an opening that's smaller than its wavelength. This leads to a 'trapped rainbow.' ... Now Vera Smolyaninova of Towson University in Baltimore, Maryland, and colleagues have used a convex lens to create the tapered waveguide and trap a rainbow of light. They coated one side of a 4.5-mm-diameter lens with a gold film..., and laid the lens — gold-side down — on a flat glass slide which was also coated with film of gold. Viewed side-on, the space between the curved lens and the flat slide was a layer of air that narrowed to zero thickness where the lens touched the slide — essentially a tapered waveguide. When they shone a multi-wavelength laser beam at the... gilded waveguide, a trapped rainbow formed inside. This could be seen as a series of colored rings when the lens was viewed from above with a microscope: the visible light leaked through the thin gold film."
So the bloody leprechaun lied to us !
You need to have two very thin pots of gold first, so you can find the end of the rainbow.
did they try tasting it?
Snowden and Manning are heroes.
Dr. Hess was later quoted as saying, "While we're obviously pleased with our success so far, we won't be satisfied until we've trapped not only the rainbow, but the leprechaun and pot of gold as well. Until then, we remain disturbingly dependent on grant money for our research."
>>You need to have two very thin pots of gold first, so you can find the end of the rainbow.
I wonder if you kidnap the scientists they'll grant you three wishes?
Tag: Leprechaun
"If humans could put Rainbows in a Zoo, they would."
--Bill Watterson, via Hobbes in Calvin and Hobbes.
Demented But Determined.
Obviously if you can see it the rainbow isn't completely contained. You can't capture a rainbow in the manner that you're thinking of because it would require a perfect vacuum (which we can mostly achieve these days), and a perfectly reflective surface (which we cannot). Every time the light bounces off of whatever you have contained it in, it will lose a bit of energy. Since it's traveling at the speed of light, you'll have enormous numbers of bounces per second and they'll quickly sap all of the energy away from the beam.
I read the internet for the articles.
(Optical computing was the answer.)
Their may be a grammatical error, misspeling, or evn a typo in this post.
Soap bubbles are better because I can make them myself, they float around in the air and they look like little gas planets with swirling atmospheres.
Seastead this.
Sounds like an old high school science experiment. Take two microscope slides (flat pieces of glass) lay one on top of another with a thin shim separating them at one end, illuminate this with a monochromatic light and see the fringes. With white light, the peaks for each wavelength would occur at different locations, resulting in a 'rainbow'. Same thing works with soap films, using internal reflection, as the film flows downwards due to gravity and becomes thicker at the bottom (wedge-shaped).
This is also a neat trick for measuring the thickness (or diameter) of a small object. Using it as the shim, count the fringes per centimeter, do some math and you know how thick it is.
Have gnu, will travel.
Selective absorption is a well known effect that takes place whenever a wave propagates in a medium where two boundary conditions have to be fulfilled at once. We observe it regularly in our lab while sending acoustic/elastic waves into a pack of slabs of material. The same thing happens with electromagnetic waves, just like Isaac Newton observed a few centuries ago. Sending the light in a direction parallel to the lenght rather than perpendicular does not discover anything new. Next post, please...
Black holes have been trapping light since the Big Bang (or "shortly afterwards" anyway, in cosmic terms).
I think God has prior art on that one. Once man can also trap gravity, strong and weak electromagnetic forces and time, I'll concede to your assertion.
Sounds like an old high school science experiment. Take two microscope slides (flat pieces of glass) lay one on top of another with a thin shim separating them at one end, illuminate this with a monochromatic light and see the fringes. With white light, the peaks for each wavelength would occur at different locations, resulting in a 'rainbow'.
What you're referring to is known as "Newton's Rings":
http://en.wikipedia.org/wiki/Newton's_rings
Interesting theory, but where does this energy go ? Is it converted to sound, heat, mass, or some other form ?
Heat.
And if we could completely "sap all the energy" away from the beam, wouldn't this imply we could create 100% effecient solar cells ?
As long as you're happy with heat as output, 100% efficient solar cells are quite trivial.
Finally! A year of moderation! Ready for 2019?
It was a very simple experiment to perform. It doesn't make any measurement of the group velocity or demonstration of trapped light (which would typically involve releasing it controllably and detecting it). The original proposal involved meta-materials to achieve a region with a negative index of refraction to use as the waveguide. They could then (hopefully) manipulate the meta-material to controllably store and retrieve light.
It seems this experiment used a simple meta-material the consisted of the glass surfaces, the 30-nm gold coating and the air gap in a Newton's rings setup. They may even have had the gold coated lens lying around and did the experiment over lunch (which just involved taking a picture). I don't think it's all that interesting until they get storage and retrieval.
So if this is the future...where's my jet pack?
As far as the reflection losses go, it's not converted to anything, it's transmitted. That's what the GP meant by "if you can see it the rainbow isn't completely contained". There's no such thing as a perfect reflector, some of the light is always transmitted through. And since we can't attain perfect vacuum, there will also be internal collisions with gaseous molecules, which can either transmit the absorbed energy via heat in colliding with other molecules, or re-transmit it as light, though possibly in a series of longer wavelengths.
As for the solar cells thing... no. That's a completely different situation. The trapped rainbow is a nearly closed system, with no continuous energy input, and the problem is that we can't make it completely closed (and if we could, it's internal entropy would then increase over time so it still couldn't be perfectly stable). Technically, I suppose all the energy can't be sapped since it's exponential decay, but the system energy asymptotically approaches 0 (and once a small enough amount remains, the fact the energy is discrete becomes important). It's about inefficient energy conversion. Far form implying that we could create 100% efficient solar cells, this is why we can't create 100% efficient solar cells.
While similar in effect to an interference patter type experiment, the actual physics behind the experiment in the article is subtly different. A 'Newtons Rings' type pattern emerges when the distance between the two (partially) reflective surfaces are a certain distance apart, coinciding with an integer value of wavelengths of the light involved. This can can, in theory, be any distance, as long as exact number of wavelengths fit inside. For example, standard interferometers can have distances as large as a centimetre, which is huge compared to the wavelength of visible light.
The effect described is based on the distance between two very reflective surfaces being smaller than the wavelength of light involved, thus preventing the light from travelling further down the waveguide. The taper on the waveguide means that as you go to shorter wavelengths of light, it can travel further, thus generating a 'trapped rainbow' of visible light inside the waveguide.
A key difference to note is that the fringe pattern generated by an interferometer type setup repeats itself as you increase/decrease the distance between the two reflective surfaces, so generating a series of lines or concentric circles. The setup with the 'trapped rainbow' will create a single rainbow pattern.