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Science Technology

First Experimental Demonstration of a Trapped Rainbow Using Silicon 79

Posted by timothy from the can-you-trap-it-in-my-tastebuds? dept.
KentuckyFC writes Back in 1947, a pair of physicists demonstrated that when a beam of light reflects off a surface, the point of reflection can shift forward when parts of the beam interfere with each other. 60 years later, another group of physicists discovered that this so-called Goos-Hanchen effect could sometimes be negative so the point of reflection would go back toward the source rather than away from it. They even suggested that if the negative effect could be made big enough, it could cancel out the forward movement of the light. In other words, the light would become trapped at a single location. Now, physicists have demonstrated this effect for the first time using light reflected off a sheet of silica. The trick they've employed is to place a silicon diffraction grating in contact with the silica to make the interference effect large enough to counteract the forward motion of the light. And by using several gratings with different spacings, they've trapped an entire rainbow. The light can be easily released by removing the grating. Until now, it has only been possible to trap light efficiently inside Bose Einstein Condensates at temperatures close to absolute zero. The new technique could be used as a cheap optical buffer or memory, making it an enabling technology for purely optical computing.
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First Experimental Demonstration of a Trapped Rainbow Using Silicon More

First Experimental Demonstration of a Trapped Rainbow Using Silicon

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  • Skittles (Score:5, Funny)

    by holmstar ( 1388267 ) on Thursday November 06, 2014 @02:39PM (#48327713)
    Now they need to implement this in candy form, so you can taste the rainbow.

  • woa.. (Score:4, Funny)

    by Charliemopps ( 1157495 ) on Thursday November 06, 2014 @02:41PM (#48327719)

    How many did they trap at once? Was it a double? Triple rainbow?!?!

  • At last! (Score:5, Funny)

    by ArcadeMan ( 2766669 ) on Thursday November 06, 2014 @02:42PM (#48327729)

    If they're able to trap rainbows, surely they're also able to trap that damn Leprechaun.

  • what? no graphene? (Score:4, Funny)

    by shadowrat ( 1069614 ) on Thursday November 06, 2014 @02:59PM (#48327835)
    how is this even possible without graphene, carbon nanotubes or metamaterials? This is just done with normal everyday stuff?

    • Re: (Score:2)

      by Cenan ( 1892902 )

      They didn't even 3D print anything. I call bullshit on this whole thing.

      • Or use an Arduino. Toooootally fake.

        • Re: (Score:2)

          by grcumb ( 781340 )

          Or use an Arduino. Toooootally fake.

          Mos def. I mean, look at the shadows along the edges, and the borders between the colours. Moiré patterns all over the place! I use Photoshop professionally, and I'm telling you, it's photoshopped [xkcd.com].

    • Re: (Score:1)

      by tkotz ( 3646593 )
      Don't panic, After RTFA, some meta materials were involved in getting the negative Goos-Hachen effect.

      • Re: (Score:1)

        by tkotz ( 3646593 )
        Nevermind the meta-materials were the old way to do this. This is just a hunk of silicon and silica. We could probably fab this with a standard lithographic technique pretty easily by finding a way to mask the bonding of oxygen with a silicon slab.
        • It's like the hipsters came along and said, "i'm not using the meta materials modern society is pushing on me, i'm only getting craft Goos-Hachen effect made the way my grandpa would make it. with dirt!"

  • Mind-blowingly cool, but... I don't get it. (Score:3)

    by pla ( 258480 ) on Thursday November 06, 2014 @03:05PM (#48327877) Journal
    Okay, I take some pride in usually understanding at least the basics behind cool science tricks like this, but I have to admit, this one just blows me away - I still don't "get", it even after reading TFAs.

    So can someone explain what really happens here? Does the light keep reflecting between the two surfaces, as though caught between two "perfect" mirrors? Or do the photons (and does this depend on wave behavior, or could we do it for particles as well) just basically stop mid-air, something like an event horizon as seen from the inside? Or something else entirely?

    / Bonus points for a car analogy. XD
    // Serious question, though... Thanks!

    • The implication, also, is that you can't actually see the rainbow I would presume, since no light is getting out.

    • Re:Mind-blowingly cool, but... I don't get it. (Score:5, Informative)

      by Anonymous Coward on Thursday November 06, 2014 @03:22PM (#48328013)
      It's a wave guide. Light travels along it, but because of the diffraction grating on the top, light gets shifted backwards as it bounces off the top. The trick is different frequencies get shifted back by different amounts, so they change the spacing of the grating over the length of the device, so that first one color gets stalled, while the rest move on and then the next stalls, until they're all stopped. However, they aren't trapped forever, the waveguide has "ohmic loses", which means light is absorbed by guide and so it eventually is lost.

      • I believe GP was specifically referring to the 'stopped' part. Considering we've always learnt that the speed of light (photons) is more or less static(ally high), it's pretty hard to accept photons just being slowed down to a halt.

        IANAP, but I've learnt from Feynman's QED lectures that reflection is not as straightforward as one tends to think it is. IIRC, reflection is more of an absorption + emission-event than a 'bouncing' event. Combining that with the text "Removing the silicon grating from the silica

    • Re: (Score:1)

      by Mr Z ( 6791 )

      Due to self-interference, the light bumps into itself on the way out, and subsequently can't get out. At least at my limited level of understanding, it's the wave-light nature of light at play here.

      I imagine at some point, the trapped photons all get absorbed and the original energy dissipates as heat.

    • Imagine a car that runs into a wall and bounces off at angle X, then hits another wall and bounces off at angle Y, and ends up in a ditch.

      This is like the wall shifting your car back x feet at the moment of impact so that when it bounces off at angle X and hits the second wall, it does so at a spot directly across from the original impact on the first wall. The second wall will also shift the car back, so when it bounces off it at angle Y, instead of ending up in the ditch it ends up impacting the same spo

  • I can't stand the phrase "so-called"! (Score:3)

    by hamster_nz ( 656572 ) on Thursday November 06, 2014 @03:06PM (#48327887)

    It has two completely opposite meanings:

    1: commonly named e.g. "the so–called pocket veto"
    2: falsely or improperly so named e.g. "deceived by a so–called friend"

    It drives me crazy!

  • In the future, instead of complaining about letting the blue smoke out, we'll complain about letting the blue light out.

  • 60 years later, another group of physicists discovered that this so-called Goos-Hanchen effect could sometimes be negative so the point of reflection would back towards the source rather than away from it.

    Don't the editors even read the freaking summary through once?! I don't know about you, but the most glaring error I usually notice is when I accidentally the sentence through and there's no verb.

    (and I thought starting a sentence with a numeral was also one of those things you're not supposed to do)

    • back v. walk or drive backwards

      Also "discovered" and "be" are there, if I was being pedantic about "no verb."

      • I don't think you can really apply the verb "back up" to light. Light is a ray that propagates without any sense of volition. Walking and driving both imply a conscious decision and effort on the part of the thing doing the walking or driving.

        "No verb in this clause," if you like.

  • Are we seeing the forerunner to light based batteries? You wouldn't actually need to trap light for memory in an optical system, you only need to have light leave at least a temporary imprint that will impact light bounced against it later.

    • Re: (Score:2)

      by swb ( 14022 )

      Solar batteries. You don't convert those photons into electricity and store that, you just store the light and then you can shine it on the solar cells when you need the power.

      I'm absolutely sure it doesn't work like this but it's an interesting science fiction concept.

      • If you are using the output to light your home, transmit data, or heat up some stew you don't need the solar cells. Toss light based computing in and you don't even need electronics anymore. I should be possible to create a reasonably efficient light motor as well, light can give up it's momentum and it has lots of it. If we can create a solar sail based on this we can create a motor. Light will bend in a magnetic field, that suggests and interaction that transfers energy, it would seem like it should be po

  • not an experimental demonstration (Score:5, Informative)

    by henryteighth ( 2488844 ) on Thursday November 06, 2014 @04:30PM (#48328547)
    The paper is entirely numerical simulation, despite what the linked blog post says. I quote: "In this paper, we numerically demonstrate an approach..". I'm not denigrating numerical simulations: I'm a computational physicist. Just, you know, RTFA?
  • I'm not clear on this, does all the trapped light get released at once when you open the gate? Like shine a flashlight at the thing for 6 months and create a blinding flash?
  • A trapped rainbow, how sad. Next thing they'll be freezing the nice pink unicorns. This is bad science and something must be done, just think of the children.

  • Light of Other Days (Score:3)

    by shutdown -p now ( 807394 ) on Thursday November 06, 2014 @05:41PM (#48329377) Journal

    If I understand the described effect correctly, they have made something very much like "slow glass" from Shaw's "Light of Other Days".

    • I thought of this too, but couldn't remember who wrote it. I remember reading one of the series he did on slow glass waybackwhen. It definitely caught my imagination then. Good stuff.

    • Re: (Score:2)

      by Lorens ( 597774 )

      At least they will have done it on purpose and not while researching a windshield for an airplane . . . Splat.

  • shortly to put their own spin on things, since they both consider themselves represented by rainbows.

  • It seems to me that the next step would be to find a way to activate and release gratings electronicall (or, even better -- optically) , rather than physically.
  • 1. Optical switching of the grating, and 2. do this in an optical gain medium. Then you CAN keep the light trapped forever and implement optical buffers, flip-flops, etc.

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