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Science

Lasetron to Produce Zeptosecond Flashes of Light 46

Posted by timothy from the yes-those-are-real-words dept.
bofh31337 writes: "Nature has an interesting story about the Lasetron. In theory, creating very short flashes of light, using high-powered lasers, you would be able to see inside atomic nuclei."
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Lasetron to Produce Zeptosecond Flashes of Light More

Lasetron to Produce Zeptosecond Flashes of Light

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  • Finally! A word to describe my attention span!
    • I think S.I. should be extended a little further to stay ahread of science. I recommend prefixes for smaller and smaller powers:

      Zeptosecond
      Chictosecond
      Gumtosecond
      Harptosecond
      Grouchtosecond

      • Re:Zeptosecond? (Score:3, Interesting)

        by JabberWokky ( 19442 )
        It's already informally been proposed [jargon.net], but interestingly enough, a Google search reveals that they are starting to be used [chemtutor.com].

        Hey... that's how these things start. I just hope they formalize it rather than stripping it away the way they did with terms for quarks.

        --
        Evan

        • Just another few centillion grouchtoseconds and they might become a real standard.

          I'm also sure any day now they'll discover the sneezy quark.

          • I'm also sure any day now they'll discover the sneezy quark.

            The "official" names are all boring. Yes, it's true - quarks have lost their charm.

            Pa dum bump.

            --
            Evan

      • Haha! This was actually the first thing that crossed my mind when I saw the headline. :P

        But why in that order? How about naming them in reverse order of importance? You'd have:

        Zeptosecond
        Gumtosecond
        Chictosecond
        Harptosecond
        and Grouchtosecond

  • Finally! (Score:3, Funny)

    by tunah ( 530328 ) <sam&krayup,com> on Tuesday February 05, 2002 @10:56PM (#2959801) Homepage
    I always wondered what color those quarks really were...
  • Important factors for photon pulses are the flux and the ability to trigger the event. We have had single photon emitters for a while. A single photon: It about as short of a pulse as you can get. Just not very bright. :-)

    What is exciting is about this result is they have achieved a very short controlled photon pulse of a non-trivial brightness.

  • WTF? (Score:2, Insightful)

    by Stone Rhino ( 532581 )
    The reason it's impossible to see inside of atoms is not because of the length of pulses, it's because the wavelength of light is larger than the size of an atom. So what I am wondering is...How the hell would length of pulses change anything? We would need higher frequency/lower wavelength light, not just short pulses of it.

    • Re:WTF? (Score:5, Informative)

      by sigwinch ( 115375 ) on Tuesday February 05, 2002 @11:51PM (#2959955) Homepage
      We would need higher frequency/lower wavelength light, not just short pulses of it.
      You're right, for single photons. Sub-single-wavelength pulses are formed from many photons, of a variety of phases and colors. On average the peaks of the various photons add up to enormous values during the pulse.

      If you've taken a class that discussed the Fourier transform, it's analogous to the impulse function, which is composed of all frequencies of sine waves. The sharper you want your impulse to be, the wider the range of frequencies you need to have in your pulse. These zeptosecond guys are using frequencies of light up to x-rays (!), which is how they get such short pulses.

    • Re:WTF? (Score:3, Informative)

      by AntipodesTroll ( 552543 )
      Yeah, but if you brush up on your Quantum Mechanics, you'll know that the shorter the wavelength, the more energy youre hitting your target with, with the photons.

      This is no good as it disturbs the target too much (the old problem of quantum uncertainty) whereas I imagine that if the pulse is short enough and of something weaker than gamma rays, they can atleast get an image before the target is unusably perturbed.

      BTW, they were talking about molecules and imaging chemical reactions, which may not be totally beyond light/soft-xrays wavelengths to do, arguably.

    • Re:WTF? (Score:5, Informative)

      by GMontag451 ( 230904 ) on Wednesday February 06, 2002 @12:04AM (#2960003) Homepage
      Short pulses mean higher frequency/lower wavelength. Since a pulse of light has to be at least one photon, and a photon is one wave packet, then the duration of a pulse determines the minimum frequency/maximum wavelength of the light in that pulse. A one zeptosecond (10^-21 s) pulse would mean that the largest possible wavelength of a photon in that pulse whould be 3x10^-13 meters. This is somewhat smaller than an atom (approx 10^-9 meters), but still larger than a nucleus (approx 10^-15 meters). So with a pulse of this duration, we would definately be able to see an atom, and we might get a rater fuzzy picture of a nucleus.

      • Re:WTF? (Score:2, Informative)

        by Joel Ironstone ( 161342 )
        yes but the minimum frequency(max wavelength) does not decessarily determine the resolving factor. If the maximum wavelength is 10^-13 meters, we end up with pulse harmonics in the 3^-13 range and smaller and can theoretically image the inside of a nuclei. This all depends on the detector, of course.

    • Re:WTF? (Score:3, Informative)

      by esonik ( 222874 )
      The idea is not to resolve sub-atomic features with visible light in way a classical optical microscopy works. The short wavelength light is needed to trigger the processes in nuclei which require high energy photons (MeV scale) and the short pulse duration is needed have the required time resolution, otherwise you would only see the final result without knowing how the system got there. Experiments with ultrashort light pulses are usually done in the so called Pump-Probe technique: With a first short light pulse (Pump) you trigger some process that you want to investigate in your sample, then after a certain time delay you shine a second light pulse (Probe) on your sample to "look" at state of the process. Doing many such Pump-Probe cycles with varying time delay between the pulses, you can "see" how the triggered process evolves (whereby "look" and "see" is not to be taken literally). In order to be able to do this your light pulses have to be shorter than the timescale of the process that you want to investigate. Chemical reactions and motion of electrons take place in the femtosecond regime, requiring fs-Lasers; nuclear reactions take place on the zeptosecond regime, requiring zs-Lasers.
  • Or does "Lasertron" sound like a perfect name for a powerful and giant robot that's the only thing on Earth that can stop a monster named "Zeptosecond", also a giant, from destroying Tokyo ?
  • I got my first good concept of a nanosecond when Adm. Grace Hopper [navy.mil] showed a foot-long piece of copper wire. That's the distance electricty can travel in that time.

    So, I'll provide an equivalent definition for the attosecond... 0.0003 nm. For comparison, a single silicon atom is 0.3333 nm in diameter.

  • One thing stands out unaddressed (Score:4, Informative)

    by CyberBlood ( 215968 ) on Wednesday February 06, 2002 @12:46AM (#2960119) Homepage
    As a physics student interested in research, I've learned that Nature generally hasn't been the most reputable science journal. In the past they've featured articles on faster than light motion, published very inaccurate results and later a story that was featured on Slashdot last April on a theorhetical quantum computer that functioned without necessarily being turned on.

    Regarless, the point in the story that seems to be missing is how they don't address the Heisenberg Uncertainty Principle. Tracking the motions of electrons around nuclei generally isn't possible. The best we would be able to know would be one component of it's angular momentum and the rest will definitionally remain unknown.

    Perhaps a better conceptualization would be the moon around the earth... It travels around the earth in a circular patter. This is about all we could know about the electron. Any other motions (like if the moon was also orbiting on a plane defined by earth's two poles) must remain unknown in quantum mechanics.

    I would say read this with caution on what they claim they'd be able to do.

    CyberBlood
    • I'm also a physics student.

      I don't think "tracking the motions of electrons around the nucleus" is what they are trying to do. Most of the time, ultrafast spectroscopy (as in femtosecond spectroscopy) is done in a "pump-probe" setup. First you pump the sample with a femtosecond pulse, then you probe it with another femtosecond pulse, delayed in time. You just have to look at the way the probe is transmitted in function of delay time to see the living times of excited states..

      I think this may be more like what they want to do.. study the nucleus dynamics, or as they say in the text, their formation or fission, ..

      I do think that you were right on one point however, when you told that they did not adress the Uncertainty Principle. What puzzles me is how do they think they are going to use zeptosecond pulses. Pulses this short must have a very large bandwith (for comparison, 5fs pulses need to have about 300nm bandwith). Dispersion will be a huge problem if they ever want to steer the beam, or even focus it.

      taxelxii
      • In the PRL they give explicit examples of experiments to do with zs pulses:

        photonuclear reactions (i.e. nuclear reactions triggered by photons): neutron photoproduction on Be (requires 1.7 MeV gamma photons), photofission of uranium nuclei.

        The proposed Lasetron would produce very short bursts of very high energy photons (gamma rays), and thus make possible the study of time-resolved nuclear reactions, like those mentioned above (however, for the uranium experiment you need urianium ion with gamma factor approx 100, i.e. an accelerator like RHIC).
    • You are teached that Nature is not reputable? What an odd subject...

      Heisenbergs uncertainy principle states that the measurement of velocity and position of a particle can only be known within a certain limit. It is possible to know one parameter very preceise at the expence of the other parameter. To be more exact
      Planck's constant = position * velocity * mass of particle
      • Heisenbergs uncertainy principle states that the measurement of velocity and position of a particle can only be known within a certain limit. It is possible to know one parameter very preceise at the expence of the other parameter. To be more exact Planck's constant = position * velocity * mass of particle

        Heisenberg's uncertainty principle is related to momenta, not velocity and mass. Particles travelling the speed of light have no mass, but still have momenta, and thus are constrained by the uncertainty principle. A massive particle has a momentum of mass * velocity, but only at speeds small compared to that of light.
        • Momenta is the product of mass and velocity.

          Particles at the speed can be considered as having all their mass converted into energy. But then the velocity is known, only the position is difficult to meassure.
          • Momenta is the product of mass and velocity.

            Not true. For massless particles, the momentum is Planck's constant divided by the wavelength.

            Particles at the speed can be considered as having all their mass converted into energy.

            No exactly. Mass is a measure of internal energy. Massless particals are massless because they have no internal energy. You could argue that a photon can be produced from an electron, converting its mass to energy, but that reaction only happens when it hits a positron, so it doesn't really count. An electron won't decompose spontaneously.

            The point that I was trying to make is that Heisenberg's uncertainty principle is not related to mass and velocity directly. It is related to the momentum of an object, which in some cases is mass times velocity times gamma (where gamma is a high speed correction factor / a function of the velocity).
      • Sorry, but in addition to MOMENTUM and position (not velocity), and pair of complementary properties can be used. In particular, Energy and Time. Since a zeptosecond pulse is so ridiculously small, the delta E must be huge.
    • The original article is in Physics Review Letters and seems sound.

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