Slashdot Mirror

← Back to Stories (view on slashdot.org)

New Way of Observing Light May Boost Info Content

Posted by Cliff on from the dance-of-the-photons dept.

md_seymour observes: "Today's Astronomy Picture of the Day from NASA has a description and image of light that can twist as well as spin, based on research from Miles Padgett and Johannes Courtial of the University of Glasgow. They and their colleagues have apparently been able to sort individual photons by their orbital angular momentum. Since this characteristic of the photon is able to take on an infinite number of values, it may be possible to pack much more information into a light beam."

39 comments

  1. we should harvest this new light to make: by theMerovingian · · Score: 2, Funny

    STAR FIBER!

    Star Fiber Router could be called the "X-wing"

    --
    "If you think you have things under control, you're not going fast enough." --Mario Andretti
  2. I hereby reserve angles/degrees/radians ... by torpor · · Score: 1

    ... cross-coordinates ... any, and all, with the digits "8008" in them, in that string ...

    --
    ; -- the corruption of government starts with its secrets. a truly free people keep no secrets. --
  3. ... oh, and ... by torpor · · Score: 0, Offtopic

    746f72706f72 as well ...

    --
    ; -- the corruption of government starts with its secrets. a truly free people keep no secrets. --
  4. For practical use by Vaevictis666 · · Score: 2

    For practical use, we need to not only be able to generate photons with a desired spin. As it is, this is still useful for cryptography, but if we want to start packing each photon (on a fibre-optic line or something) with a base 64 value instead of a base 2 value (for example) we need to be able to reliably generate the photon with the correct spin out of the 64. But once that goes say hello to cheaper internet speeds :)

    1. Re:For practical use by Anonymous Coward · · Score: 0

      For practical use, we could use it's quirkyness to see earth sized planets orbiting stars without building monsterous interferometers.

      And seeing those plantes would obviously provide us with a spectra, and thus very broad atmospheric sample. Which certainly might be interesting.

    2. Re:For practical use by Yazeran · · Score: 2, Informative

      For practical use, we could use it's quirkyness to see earth sized planets orbiting stars without building monsterous interferometers.

      Sorry nope. This would do us no good in detecting planets at interstellar distances. First of all, you still need large interferometers (or mirrors) to resolve small angular distances (read planetary orbits at interstellar distances). Secondly, ordinary light (from stars and planets etc. is randomly polarised and the orbital angular momentum would be distributed randumly according to some statistical energy distribution function (there are several and i don't know enough quantum physics to tell which one). Therefore the orbital angular mmentum would not carry any information. You need lasers or similar stuff to encode the angular momentum with information, natural light does not work.

      Yours Yazeran

      Plan: To go to mars one day with a hammer.

    3. Re:For practical use by Anonymous Coward · · Score: 0

      Supposedly, from what I've read, the dust inbetween the objective and us would do the job. This allows us to build a small device canceling out the star, revealing only the photons which came from the planet. And those, scattering off the planet would carry spectral information. Which would probably take quite a while to build, but long exposures have been done with hubble, so why not?

  5. Some light humour :) by stjobe · · Score: 3, Funny

    Measuring the orbital angular momentum of single photons is a "brilliant" achievement, says Keith Burnett of the University of Oxford.

    Not that I understand one bit of what they're talking about, though :)

    --
    "Total destruction the only solution" - Bob Marley
    1. Re:Some light humour :) by torpor · · Score: 1


      Well, for one, thats a 'pun', since 'brilliance' is of course a type of optical quality, and its use in science is derived from its context in gemology, where a 'brilliant' (gemstone) often is carved in a manner which implies orbital angular momentum, which is incidentally, or 'was' (in the days of gemology) a measure of its worth, since its supposed to be difficult to carve a diamond in such a manner that its outer edge implies such things ...

      Those wacky scientists.

      --
      ; -- the corruption of government starts with its secrets. a truly free people keep no secrets. --
    2. Re:Some light humour :) by stjobe · · Score: 1

      Seeing as I'm totally in the dark when it comes to gemstones, I'll take your word as enlightenment.

      However, what my comment about my ignorance referred to was the subject matter of the article, that is the orbital angular momentum of photons, which is still somewhat murky to me.

      But then again I might not be very bright...

      --
      "Total destruction the only solution" - Bob Marley
    3. Re:Some light humour :) by MindStalker · · Score: 1

      angular momentum = mass * (angular velocity)
      angular velocity is velocity divided by radius of rotation.

      I'm not possitive about orbital angular velocity, but it seems as though it refers to the fact that the center point of the rotation is moving. So basically a point with an orbital angular velocity is spiraling along.

  6. infinite? by Tom7 · · Score: 2, Redundant

    Since this characteristic of the photon is able to take on an infinite number of values,

    Not really though, right? Such values are discretized in the sense that the Planck length discretizes distance, right?

    1. Re:infinite? by Anonymous Coward · · Score: 2, Informative

      There's an infinite number because any integer multiple of the base value is possible.

      To use your parallel, Planck length places a bound on fractions of 1 meter, but not on multiples of 1 meter.

    2. Re:infinite? by rpresser · · Score: 1, Redundant

      As the other poster said, you can have L = +1, +2, +3, ..., -1, -2, -3 ... to any value. Which makes me wonder though, does a high L mean the photon carries more energy?

    3. Re:infinite? by omega_cubed · · Score: 2, Informative

      Yes, actually an infinite number of values. The same way that the integers in discrete, but infinite in number.

      --
      Engineers also speak PDE, only in a different dialect.
    4. Re:infinite? by Mr+Foot · · Score: 0, Redundant

      I wouldn't expect it to carry more energy because a photon is massless. At least classically rotational kinetic energy is zero for a massless particle. Though there may be some other quantum mechanical effect going on, the photon is hardly classical after all. It's a very interesting question...

    5. Re:infinite? by Anonymous Coward · · Score: 0

      photon's aren't massless.

      They have mass.

      Hence items such as the solar sail work (and no its not powered off the solar wind, else it wouldn't need to be reflective), and more importantly, a massless photon would not be affected by gravity, items such as gravity lensing and black hole event horizons show that photons have mass. I agree its miniscule, but the mass is still there.

    6. Re:infinite? by Mr+Foot · · Score: 1

      Photons carry momentum which they can transfer to a solar sail, but they massless as far as we can tell.

    7. Re:infinite? by Anonymous Coward · · Score: 1, Interesting

      I had a problem with that claim too.
      I think they should have said the number of encodable bits is reliant on the sensitivity of our measurments. otherwize one could say that a 5 foot long piece of rope has infinate encoding capacity.
      Well duhh,, 5 / 3 = 1.666666666666666666666666~~

    8. Re:infinite? by Anonymous Coward · · Score: 0
      You have an interesting grasp of physics. I believe you might have a good case for requesting a paritial refund on your diploma as you clearly have been overcharged for what you got out of it.

      Photons have zero rest mass.

      Photons have energy, momentum, and do transmit force (p = E/c, or p = h/wavelength). See Compton's 1927 Nobel prize work, or any standard QED description of the electromagnetic force.

      Massless photons are affected by gravity. See Einstein's 1915 General Relativity work, and Eddington's 1919 solar eclipse measurements.

    9. Re:infinite? by rpresser · · Score: 1

      Thank you for confirming my understanding so far. (Somebody please mod that AC up as informative.) But the question remains: does the angular momentum carried by the photons affect the energy? I mean, they're talking about stuffing bits into this; anything that carries information usually requires energy. By the way, there is a lot of new work in gravitational lensing. The Hubble has discovered a couple dozen definite lenses; some of them even show some distant objects that are not conventionally visible.

    10. Re:infinite? by Anonymous Coward · · Score: 0

      You'd have to wait a long time to see structure that extended over a parsec though, so the rate that such information could be transmitted would be limited..

      </Talking out my ass>

  7. Old News by Rubyflame · · Score: 1

    This is just circularly-polarized light, isn't it? Shine a laser through a polarizer and a quarter-wave plate, and that's what you get.

    --

    All it takes is nukes and nerves.
    1. Re:Old News by Anonymous Coward · · Score: 0
      RTFA

      Explanation: Light is more complicated than we thought. When astronomers measure light, they are usually concerned with its direction, energy, and spin polarization (sometimes). Recently, however, it has been more broadly realized that photons can also have orbital angular momentum (OAM),

  8. No. by Anonymous Coward · · Score: 4, Informative

    No, they're different.

    Take a beam of circularly-polarized light (without orbital-angular-momentum), freeze time in your imagination, and look at the E-field vectors along the beam. The E-field vectors all point in the same direction. Over time they rotate around the beam axis -- that's what circular polarization means -- but the E-field-vectors are always aligned along the entire length of the beam.

    Now instead imagine a beam of light with orbital-angular-momentum, and again freeze the beam in your imagination. Now the E-field vectors make a helix along the beam.

    You get circularly polarized light by passing a beam through a polarizer and quarter-wave plate. You get light with orbital angular momentum by spinning the light source around the beam axis.

  9. A bit more information from Scientific American by UnknowingFool · · Score: 4, Informative

    There's a short article about this property of light in this month's edition of Scientific American. Apparently this propery isn't new but rather largely ignored.

    --
    Well, there's spam egg sausage and spam, that's not got much spam in it.
  10. Translation: by Anonymous Coward · · Score: 0

    Not a circle, like a 'corkscrew.'

  11. I want. by hackwrench · · Score: 0

    I want technology based on this stuff yesterday. Also, get SETI looking for these types of signals.

  12. Lots of bits on ONE PHOTON!!! by harrkev · · Score: 1

    Wow. First, let's assume linear polarization. The polarization angle could vary between 0 and 179.999 degrees. If the "twist" of the light could be considered as an "amplitude," then we could do a variant of QAM on a single photon. Depending upon how sensitive the receiving equipment is, and how precise the transmitting equipment is, it should be possible (in theory) to then encode at least 4 bits in one single photon.

    Of course, building such a transmitter/receiver would be an engineering nightmare. But we can dream...

    --
    "-1 Troll" is the apparently the same as "-1 I disagree with you."
    1. Re:Lots of bits on ONE PHOTON!!! by Anonymous Coward · · Score: 0

      Is this photon-with-angular-momentum thing kind of the same as transmitting radio waves with helical (corkscrew?) antennas?

  13. scientific american article by mdmarkus · · Score: 2

    Scientific American has this article as well. I admit, i'm still scratching my head over it after reading it when i got the paper version last month...

  14. Total energy and mass? by stonewolf · · Score: 3, Interesting


    Is orbital angular momentum (OAM) a bit of energy added to the photon, or is it just a redistribution of the "normal" energy of the photon? If it is a redistribution then does a photon with OAM have a different wavelength than a photon with the same energy but no OAM?

    Does generating a photon with OAM transfer angular momentum from the generator to the photon? That is does emitting an OAM beam cause the source to spin?

    Many questions that boggle my mind.

    Stonewolf

  15. Upside-down ray? by Anonymous Coward · · Score: 0

    As Far as i can tell, this means you could actually build a laser cannon that upends targets? Cool. In a gravitational field, that could hurt seriously at lower intensities than the usual "vaporisation" idea of lasers, right?

    1. Re:Upside-down ray? by Anonymous Coward · · Score: 0

      Holy crap- imagine a cluster of intense beams with different orbital angular momenta hitting an extended object with some rigidity (i.e.things that are solid), it would rip the solid apart as different parts of the solid tried to rotate in different directions!

      Clearly, you could build a better disintegrator beam with this than a boring old "vaporise you one cubic micometer at a time" laser....

    2. Re:Upside-down ray? by Anonymous Coward · · Score: 0

      Less vicious uses? Perturb the path of an incoming missile or bullet - much lower energy cost than destroying them, right?

    3. Re:Upside-down ray? by Anonymous Coward · · Score: 0

      hmm... tesla vindicated again?

      If one can produce a beam of E.M radiation with orbital angular momentum, and that angular momentum can be transferred to matter, than one could focus a beam on a viscous fluid and start up a whirlwind or storm?

    4. Re:Upside-down ray? by Anonymous Coward · · Score: 0

      presumably would only work if the missile or bullet was travelling at speed through a viscous medium, but that's most of them...