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Lasers Approach Their Ultimate Intensity Limit

Posted by samzenpus on from the biggest-pointer dept.

Flash Modin writes "Death Star style superlasers? Don't bet on it. High-power lasers currently in development appear to be nearing the theoretical laser intensity limit, according to new research set to be published in the journal Physical Review Letters. Ultra-high-energy laser fields can actually convert their light into matter as shown in the late '90s at the Stanford Linear Accelerator (SLAC). This process creates an 'avalanche-like electromagnetic cascade' (also known as sparking the vacuum) capable of destroying a laser field. Physicists thought it might be a problem for lasers eventually, but this work indicates the technology is much closer to its limit than researchers believed. A preprint is available here."

13 of 384 comments (clear)

  1. Maybe, maybe not by mcgrew · · Score: 4, Interesting

    Creating light from matter is rather ordinary in terms of physics, as can be seen in nuclear explosions

    Or even running out of lighter fluid.

    The SLAC experiment was just a singular event, but as lasers reach higher intensities the electric fields produced will increase as well and the team says that when they reach a critical intensity a cascade effect will occur as a result. The electron-positron pair is accelerated by the laser field itself at such high energies that they emit photons capable of spawning new pairs and continuing the process.

    Maybe that's how the death star works? Besides, it isn't explicitly stated anywhere in the movies that the death star is a laser.

    Also, they're not talking about a single laser, they're talking about colliding two laser beams.

    --
    Free Martian Whores!
    1. Re:Maybe, maybe not by erroneus · · Score: 5, Interesting

      Actually, from what I can see, the blaster, the death star's beam, the lightsaber and even the beam weapons on the clone wars gunship turrets seem to work on something other than "laser." They seem to operate on energized particles or energy that is transformed into a mass-like state. In the case of the death star, it would seem to explain why merging many beams from different angles could actually result in a single beam going in yet another angle.

      In any case, you can see blaster bolts travel... they seem to fly at around arrow speed. The fact that they emit light leads people to think "laser" when in reality, you can't see a laser in most cases unless there is interference in the air. (BTW, did you ever notice that headlights seem to be less effective at night after a rainfall? That's because the roads are wet and more reflective... the light gets reflected away from your eyes and so you can't see the light bounce back to your eyes.)

      Worse still, the term "laser sword" is actually used in Star Wars which doesn't help things at all. Young Anakin identifies Qui Gon as a Jedi because of his "laser sword." On one hand it is forgiveable because he's a kid, but on the other hand, he's a genius kid and should know better. In any case, lightsabers have a shadow (because of some sloppy film editing) but ostensibly because they are not lasers but an energy/matter transition state where energy is made to behave as matter. (Though only shown in games and cartoons, energy "bridges" are used to create temporary walkways using a technology similar to that used in lightsabers)

      It's all fiction anyway, but it helps to try to understand the technology imagined in these fictions. The technologies imagined in SciFi are quite often candidate for implementation in our present or near future.

    2. Re:Maybe, maybe not by waives · · Score: 2, Interesting

      Someone with a nick like yours should really know better.

      Just as chemical reactions conserve the number of atoms, nuclear reactions conserve the number of subatomic particles.

      Only in a matter/antimatter reaction will the number of massive particles be changed.

    3. Re:Maybe, maybe not by scorp1us · · Score: 2, Interesting

      Well in Star Trek, they refer to phasers as "colonizing energy"

      Here's my take. In SW, is an anti-matter particle beam. The glow you see is antimatter atoms reacting with the interstellar medium, which is less than total vacuum. Hence, you get some reactions (and losses) en route. This is what you see. It is also the only medium to generate that violent a reaction that quickly. A laser would simply heat it. And the problem with lasers if you have to be able to dissipate your inefficiencies. So if you have a 33% efficient laser of 1MW, you have to be able to dissipate 2MW yourself. This means everyone on the Death Star would cook, and it would blow itself up twice as fast as Alderan. (Assuming Alderan's the DS's thermal properties are the same, etc)

      You can also explain the beam consolidation as simple vector math, as well as the slow propigation to target.

      This does leave a problem of how light sabers work without blowing up the user the second it cuts something made of matter.

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    4. Re:Maybe, maybe not by Fieryphoenix · · Score: 3, Interesting

      No, none of the matter was converted to energy. Chemical bonds were broken apart, and the energy that comprised them was dissipated as heat and light. Not one proton, neutron or electron was destroyed in the process.

    5. Re:Maybe, maybe not by John+Meacham · · Score: 3, Interesting

      In truth, it does always bother me how easy it seems to 'blow up' planets in fiction. If you think about it, the amount of energy required to blow up a planet would be equivalant to launching every bit of the earth into space, think about the amount of energy involved in just getting the tiny space shuttle into space, then think about doing that for mount everest, then think about doing that for mount everest about 10,000,000,000,000,000,000 times. That is how hard it is to blow up a planet (very roughly)

      http://qntm.org/destroy has some more good information on destroying the earth.

      --
      http://notanumber.net/
    6. Re:Maybe, maybe not by toppavak · · Score: 1, Interesting

      To put the 1e32 Joules of energy in perspective, the energy density of matter-antimatter annihilation is roughly 9e16 J/kg. The amount of antimatter/matter reaction mass necessary to accelerate your 100km asteroid to 3% of the speed of light is therefore 1e32 / 9e16 = 1e15 kg or approximately the mass of 9-10 billion Mount Everests.

    7. Re:Maybe, maybe not by EETech1 · · Score: 2, Interesting

      Wouldn't the little bits and pieces all attract back together again eventually if they were not at escape velocity? Like the big bang / big crunch theory? If you didnt blow it apart enough to get away from itself, wouldn't gravity win in the end?

      So you might have blown it to pieces, but the pieces would eventually collect back together due to the mass and proximity? Wouldn't you have a large plume of earth chunks say maybe 1000 times the size of earth, but with nearly the same gravitational force, so it would then begin pulling itself back together?

      So I'm guessing that it might take more energy to permenantly blow it to pieces than to blow it apart, and have it all come crashing back together? But im only guessing. (well guessing and hoping someone can clarify)

  2. Re:matter from light? by Anonymous Coward · · Score: 1, Interesting

    Electron-positron pairs. Seems to me that this effect could be used to create a high-energy, LASER pumped, near light-speed particle beam, with the added possibility of electron-positron annihilations at the point of impact.

  3. Re:Death Star style superlasers? Don't bet on it. by jd · · Score: 2, Interesting

    That part I wasn't waiting for, but actually this light-into-matter might be exactly what you want. Light is messy for this, but if you can have your lasers converge and convert into a stream of antimatter particles, things would surely get more interesting.

    The one thing this does bugger up big time, though -- I spent HOURS trying to work out how bright headlights would need to be to propel a car backwards. The headlights would be so totally over this limit that you'd end up smashing the headlight covers in the attempt. It would also cover the street with newly-formed matter. Damaging the street is a ticketable offense.

    --
    It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
  4. Galactic History by Ken Burns by handy_vandal · · Score: 2, Interesting

    You're joking, right? About how "Ken Burns will revisit that period of the galactic history and we'll get a more neutral viewpoint of the conflict."

    For "more neutral viewpoint", substitute:

    "Ken sank his heart and soul into this thing, and it's obvious that he's still grieving for Alderaan."

    Don't forget the soft, heart-felt banjo-centric soundtrack.

    --
    -kgj
  5. Re:matter from light? Transporter? by KDN · · Score: 2, Interesting

    So we are approaching the intensity at which light turns into matter. One step (of many) to building a transporter?

  6. Re:Limits? Ha! by GooberToo · · Score: 2, Interesting

    Its been suggested some planes in WWII, in dives, were actually breaking/transitioning the sound barrier. This is why many planes never pulled out of their dive and crashed into the ground. The reason being, not enough control surface to function with the shock waves (compressibility) to allow for maneuvering to avoid their fate. This was, in fact, a fate repeated by many test pilots who attempted to break the sound barrier. It wasn't until the flying control surface was created that the problem was licked.