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Nanoantennas Can Change Phase of Light

By - Source: Purdue University | B 17 comments

Researchers at Purdue University found that arrays of plasmonic nanoantennas can be used to manipulate the phase, a wave shape, of light as it propagates.

The scientists now believe that they have found a path that could enable more powerful microscopes, telecommunications and computers. Specifically, the discovery is expected to have effects on technologies for "steering and shaping laser beams for military and communications applications, nanocircuits for computers that use light to process information, and new types of powerful lenses for microscopes."

The research builds on a previous modification how scientists have described how light reflects and refracts or bends while passing from one material into another, which is referred to as Snell's law. Each material has its own refraction index and all natural materials show positive refraction indexes. However, Purdue's nanoantennas can change the refraction and even achieve negative angles.

"Importantly, such dramatic deviation from the conventional Snell's law governing reflection and refraction occurs when light passes through structures that are actually much thinner than the width of the light's wavelengths, which is not possible using natural materials," said Vladimir Shalaev, scientific director of nanophotonics at Purdue's Birck Nanotechnology Center. "Also, not only the bending effect, refraction, but also the reflection of light can be dramatically modified by the antenna arrays on the interface, as the experiments showed."

According to the scientists, the nanoantennas feature V-shaped structures that are made of gold and are placed on top of a silicon layer. The antennas are 40 nm wide. Shalaev said that they are able to transmit light through an ultrathin "plasmonic nanoantenna layer" that is about 50 times smaller than the wavelength of light it is transmitting. "This ultrathin layer of plasmonic nanoantennas makes the phase of light change strongly and abruptly, causing light to change its propagation direction, as required by the momentum conservation for light passing through the interface between materials," Shalaev said.

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  • -6 Hide
    Anonymous , December 28, 2011 7:18 PM
    Esto si es muy impresionante...sera la nueva era?
  • -4 Hide
    jackbling , December 28, 2011 7:51 PM
    Love to see a law broken; I like to think it stimulates the imagination of researchers in the relevant field, it has to be invigorating to have that barrier lifted.

    Even tho in this case it would appear they just amended the law.
  • -4 Hide
    rawful , December 28, 2011 8:29 PM
    What is a negative angle?
  • -4 Hide
    doomgaze3 , December 28, 2011 8:33 PM
    How soon until I can buy an invisibility cloak?
  • 7 Hide
    Haserath , December 28, 2011 8:34 PM
    rawfulWhat is a negative angle?

    An angle greater than the angle of refraction, I would assume.

    Refraction is based on the speed of light through a medium.
  • 1 Hide
    jgutz2006 , December 28, 2011 8:56 PM
    jackblingLove to see a law broken;
    Theft included? :-)
  • 5 Hide
    sseyler , December 28, 2011 11:20 PM
    jackblingLove to see a law broken; I like to think it stimulates the imagination of researchers in the relevant field, it has to be invigorating to have that barrier lifted.Even tho in this case it would appear they just amended the law.

    jackblingLove to see a law broken; I like to think it stimulates the imagination of researchers in the relevant field, it has to be invigorating to have that barrier lifted.Even tho in this case it would appear they just amended the law.


    Snell's law was never "broken". Snell's law is based on classical models of the behavior of light at interfaces. Saying "Snell's law was broken (by Purdue researchers)" is a statement that shows a profound misunderstanding of physics being talked about. I'm not blaming people for misunderstanding, because much of the fault of scientific ignorance and confusing is a consequence of poor reporting and communication. Albeit things like this point to a gross lack of scientific literacy among the general public.
  • 1 Hide
    kronos_cornelius , December 29, 2011 12:28 AM
    I am totally ignorant about this. But sounds interesting. Can Mr. Perry extend the article to review what Snell's law is, why sseyler thinks no law was broken, and what he means by a negative angle ?

    I'll come back to this article later to check.. meanwhile I'll check if TR and Wired for more info on this.
  • 2 Hide
    Anonymous , December 29, 2011 7:51 AM
    @kronos_cornelius
    Negative refraction index:
    http://www.rikenresearch.riken.jp/images/figures/hi_3837.jpg
  • 0 Hide
    freggo , December 29, 2011 2:11 PM
    frozonichttp://d37nnnqwv9amwr.cloudfront.n [...] 751942.pngthats all we need to do


    Well, NASA is actually using that on a few probes out there !
  • 0 Hide
    freggo , December 29, 2011 2:23 PM
    It has to make you wonder what is going thru the mind of an engineer involved in this type of research.
    They are building 'structures', functioning perfectly, that they will never be able to actually 'see'.

    Imagine them at a party, some chick casually asks 'so what do you do for a living'. The response is likely to give her a migraine and she is off to the bar. :-)

    I think it is cool that some scientists take this path, also a shame that it also means that most of your initial funding will likely be from various military concerns. You know, the 'defense' people...
  • 2 Hide
    buzznut , December 29, 2011 5:23 PM
    Actually I took Physics II this semester and we dealt with Snell's Law for about 4 weeks. But I must admit, I'm not sure what is meant by negative angles.

    The angle of refraction is what happens when light passes from one medium to another. They have to be two different materials with 2 different refractive indexes. The refraction is caused by light either slowing down or speeding up as a result of the medium change.

    None of that explains how one acheives a negative angle.

    Quote:
    Each material has its own refraction index and all natural materials show positive refraction indexes. However, Purdue's nanoantennas can change the refraction and even achieve negative angles.


    I think what should be here instead of "negative angles" is "negative refraction indexes." Linking a relevant Wiki:

    http://en.wikipedia.org/wiki/Refractive_index
  • 0 Hide
    juxtaposer , December 30, 2011 6:50 AM
    In a typical refraction example, say air for y>0 and water (denser) for y<0, a light ray from air bends at the air-water interface and continues in generally the same direction: that is, the direction vectors of the incident and refracted rays are in the same quadrant. (If the incident ray comes in from the upper left, (-x,+y), and goes rightward and downward towards the origin at (0,0), the refracted ray goes out (+x,-y), also rightward and downward. The angles are measured between the -y axis (the normal to the interface) and the ray direction vectors.)

    Snell's Law says that Ni sin(theta_i) = Nr sin(theta_r), where i is for the incident ray (in air), r is for the refracted ray (in water), and the N's are the indices of refraction.

    Since sin(-theta_r) = -sin(theta_r), I would think that a negative refraction angle should represent a ray going out with one component reversed, e.g. downward, but leftward. (The alternative would be upward and rightward, which would be a reflection back into the air.) The refracted ray would point in a different quadrant. For example, if you were standing on the moving end of a diving board and looked down into the water, you normally see the bottom of the pool in front of you; but, with a negative refraction angle, you would look forward and down and see the pool floor under the diving board and distorted.

  • 0 Hide
    yumri , March 4, 2012 3:47 PM
    what juxtaposer said was cool and interesting but to complex for me to understand so can someone explain it correctly but probably in more words as i need it in simpler terms for my layperson's mind
  • 0 Hide
    juxtaposer , March 4, 2012 4:42 PM
    Anonymous@kronos_corneliusNegative refraction index:http://www.rikenresearch.riken.jp/ [...] i_3837.jpg


    An excellent picture. (I missed it before.)
  • 0 Hide
    juxtaposer , March 4, 2012 4:43 PM
  • 0 Hide
    juxtaposer , March 4, 2012 4:48 PM