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Tapering Waveguide Captures a Rainbow 72

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."
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Tapering Waveguide Captures a Rainbow

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  • Leprechaun (Score:5, Funny)

    by daveime ( 1253762 ) on Saturday November 28, 2009 @03:54PM (#30256310)

    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.

    • by ShakaUVM ( 157947 ) on Saturday November 28, 2009 @04:04PM (#30256366) Homepage Journal

      >>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

    • We all assuming its pots of real gold at the end of the rainbow. Leprechauns lied once, they'll lie twice. I saw its pots of fools gold.

      I think the US Gold Reserve isn't in Fort Knox. Its at the other side of the rainbow too. ;)

    • by SEWilco ( 27983 )
      It is now apparent that the gold is in a bucket, not a rounded pot.
  • But the ends still technically had gold beneath them.

  • skittles (Score:4, Funny)

    by Lehk228 ( 705449 ) on Saturday November 28, 2009 @03:56PM (#30256322) Journal
    did they try tasting it?
    • by Yvan256 ( 722131 )

      Tastes like shiny.

      •     You obviously haven't eaten enough acid. Eat these two sugar cubes, and tell me what the rainbow tastes like in about 30 minutes.

            -Dr JWSmythe

            (if only all prescriptions were this easy, or entertaining.)

  • by Broofa ( 541944 ) on Saturday November 28, 2009 @04:03PM (#30256352) Homepage
    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."
  • by Dr. Eggman ( 932300 ) on Saturday November 28, 2009 @04:07PM (#30256378)
    "If humans could put Rainbows in a Zoo, they would."
    --Bill Watterson, via Hobbes in Calvin and Hobbes.
  • Okay, aside from the obvious "nifty" factor, can someone explain in dummy-terms what other cool stuff this might lead to? I realize that research isn't necessarily about making immediately useful things, but surely someone knows of some fantastic avenues this might lead towards?

    Not trying to downplay any significance here, just looking for some insight from someone more familiar with what's going on. :)

    • Re: (Score:1, Funny)

      by Anonymous Coward
      Rainbow coloured porn that's trapped in meta-materials, of course.
    • Re: (Score:1, Offtopic)

      Nevermind, I just managed to RTFA. :D

  • by Baldrson ( 78598 ) * on Saturday November 28, 2009 @04:29PM (#30256516) Homepage Journal
    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.
  • by PPH ( 736903 ) on Saturday November 28, 2009 @04:32PM (#30256542)

    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.

  • 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...
    • I don't know much about selective absorption in acoustic waves but this process relies on a waveguide. While waveguides occur in acoustics, I don't think you can get as much energy into the evanescent wave, which is critical to the large group velocity reduction. But, acoustics isn't my field so perhaps you could correct me if I'm wrong.
      • Elastic wave equations can be transformed into Maxwell's electromagnetic field equations and viceversa, see for example W. Chew's textbook [] for a demonstration. Funny, isn't it ?!?
        • Well, I suppose wave equations are wave equations ;) but I'm still always a bit amazed at how general the mathematical descriptions of physical systems are.
    • I did read the article (which is one page, and contains nothing complicated). It's *exactly* a Newton's rings experiment, and has practically nothing to do with metamaterials, nor with an "adiabatically-tapered waveguide", as the article claims. Looks to me as though New Scientist did some _very_ sloppy reporting, and /. got snookered into picking it up as real research.

  • by Interoperable ( 1651953 ) on Saturday November 28, 2009 @05:22PM (#30256830)

    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.

  • It's in, well, Towson, which is in Baltimore County, MD.
  • 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
  • And then, the rainbows turned on us, the seven frequencies combining their harmonics into a single meta-Frequency

    A frequency . . . of DEATH!!!!!


Karl's version of Parkinson's Law: Work expands to exceed the time alloted it.