Wednesday, August 11, 2010

Lasers reaching their limit

Somebody is going to have to break the news to Darth Vader. His Death Star's planet destroying potential is going to be way behind schedule. Research scheduled to be published in an upcoming issue of the journal Physical Review Letters shows that lasers are already close to reaching their maximum intensity and that the next generation of lasers currently being developed might be able to reach that limit.

In 1997, an experiment at SLAC sent 47-billion eV electrons from its 2 mile long accelerator and collided them with a one trillion watt green laser to create a monstrous electromagnetic field. When the electrons and the photons from the laser impacted, they created higher energy gamma-ray photons, these gamma-ray photons then collided with photons in the laser beam again and shattered the vacuum as matter was spontaneously created from light within the experiment.

Creating light from matter is rather ordinary in terms of physics, as can be seen in nuclear explosions. But the SLAC experiment was the first to produce the opposite, and while the effect had been expected for some 50 years, the equipment hadn't existed to test it experimentally. It is known amongst physicists as creating "spark in a vacuum." When the electromagnetic field has enough energy, light becomes matter as a positron-electron pair is produced.


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. In fact, their estimations indicate that even a single such pair can completely destroy the laser field as the energy created from the pairs can equal that of the laser.

From the paper (available in preprint on the arXiv):

"At high laser intensities interaction of the created electron and positron with the laser field can lead to production of multiple new particles and thus to formation of an avalanche-like electromagnetic cascade."

Physicists have suspected this cascade effect could limit the intensity of lasers, but these new calculations show that the effect will likely be seen in lasers already being built like the European laser projects ELI (Extreme Light Infrastructure) and XFEL (X-ray Laser Project).

45 comments:

  1. "Creating light from matter is rather ordinary in terms of physics, as can be seen in nuclear explosions." Yes, and also in a candle
    Aeg

    ReplyDelete
  2. Actually, all potential chemical energy is stored as mass, so yes, a candle does lose a very, very small amount of mass as it burns. It's only in nuclear reactions that we see direct conversion of significant amounts of matter to energy (or vice-versa, especially in supernovae).

    ReplyDelete
  3. This matter is only being created when two lasers collide and the energy from both is combined, correct? If you were to have the lasers collide at some angle other than straight on wouldn't the matter be fired out?

    ReplyDelete
  4. Looking at the way the Death Star fired, I would guess they are using this effect to make some kind of coherent meson beam.

    ReplyDelete
  5. I never thought I'd see a resonance cascade, let alone create one.

    ReplyDelete
  6. What mater is created? Hydrogen perhaps?

    ReplyDelete
  7. A candle is not a nuclear reactor. No mass is lost in a burning candle. The energy released from a burning candle is produced by oxidizing the hydrocarbons in the wax. The photons (heat and light) are a result of the lost energy in the chemical bonds, not lost mass. You don't end up with different atoms after a candle burns, just different arrangements of the same atoms. All the 'lost' mass can be accounted for by collecting the gases that are released.

    ReplyDelete
  8. Unless I'm wrong and my HS physics teacher was just being silly. ;-)

    ReplyDelete
  9. Yes, thanks for the comments. Anytime you convert matter into light you lose some mass. We made a correction to the post.

    ReplyDelete
  10. The energy in the chemical bonds amounts to mass. Very little of it, but still mass.
    http://en.wikipedia.org/wiki/Conservation_of_mass#The_mass_associated_with_chemical_amounts_of_energy_is_too_small_to_measure

    ReplyDelete
  11. Does this mean we are one step closer to building star trek replicators?

    ReplyDelete
  12. When a candle burns it is a standard hydrocarbon flame. The "energy" given off is not produced by the loss of mass. The energy given off is "in" the chemical bonds (potential energy) of the hydrocarbon, it was put there by the process that created the hydrocarbon from the component hydrogen and carbon, most likely photosynthesis. The hydrogen, oxygen, and carbon just move around. The energy came from the sun.

    In nuclear fission, atoms are broken and the forces holding them together are released. The energy is coming from the destruction of matter.

    ReplyDelete
  13. RE: "Not exactly. When a candle burns, the same amount of matter exists after as there was before, it just changes from one form to another. In a nuclear explosion, some matter is actually annihilated and converted into energy"

    for practical purposes, sure ... but the Burning Candle's photons which are also particles with mass came from where? Atoms... in the candle or air or both... The system had better lose the photons' worth of mass after the candle goes out or you have a serious accounting problem.

    ReplyDelete
  14. Wait,

    I thought photon was a boson which means that essentially, they don't interact with each other... I've never taken particle physics, but how can a photon collide with another photon? I mean I can understand how the "intensity" can be combined with multiple photons being in phase with each other hence increasing the local electric field, but collision? This may not be the best term to be used....

    ReplyDelete
  15. Is this a case of non-liner effects taking over, showing that so called 'point' particles are really EM Soliton waves? You get the EM field high enough and the system goes non-linear.

    ReplyDelete
  16. "The system had better lose the photons' worth of mass after the candle goes out or you have a serious accounting problem. "

    photons are massless.

    ReplyDelete
  17. Acctually, mass and energy is just two metrics of the same thing - the very concept of converting one into the other is meaningless. Yes, even light has mass (but no rest mass, since it never rests) and making "matter" out of light (or vice versa) is just another form of energy conversion, albeit one that converts bosons to fermions ( or vice versa). I hope that was clear!

    ReplyDelete
  18. So in the future lasers will have limited range, and essentially become a particle beam with more or less the same amount of energy in it as the laser originally had?

    Correct me if I'm wrong, but while being hit by that powerful a laser would be bad news, so would being hit by a particle beam consisting of nothing but positrons and electrons at relativistic speeds, pairs which I'm guessing will annihilate one another upon impact releasing their energy again.

    ReplyDelete
  19. For nuclear fission you can also say that you have the same number of protons and neutrons afterwards. But you can measure a loss of mass. The nuclei are stronger bound together. There is less energy stored in the resulting atoms; it is also said that the binding energy of the resulting atoms is higher. The energy difference is emitted during fission. The mass is always equivalent to the stored energy (E = m c²), this is why the mass is reducing.
    Same happens for the burning candle. The products of the chemical rection have a higher binding energy, resulting in a lower mass. This is not relevant in practice though, since the mass difference is extremely small.

    ReplyDelete
  20. Just a wild thought. Think of exceeding the critical intensity as analogous to the inverted population of excited electrons that is required for a normal laser to lase. I'm wondering if the cascade of electron-positron pairs could be produced so that they were all in phase with each other. Perhaps then we'd have a MASEP (Matter Amplification by Stimulated Emission of Particles)?

    Sincerely Marc

    ReplyDelete
  21. energy is matter, matter is energy.
    the total quantity of energy / matter
    is the same before and after, the only
    confusion comes from innacuracy of
    detection and measurement of the before
    and after states... failure to detect
    the truth is not a failure OF the truth.

    now, the real mind blower, the real real
    _REAL_ interesting stuff is biology....

    does it not blow your mind that the passage
    of energy through almost every system yet
    found increases the disorder of that system.
    the entropy of that system, and yet what is
    life? but a physical system? and how does it
    react to the passage of energy through it.

    IT BECOMES MORE ORDERED WITH THE PASSAGE
    OF ENERGY THROUGH IT. the biological system
    avoids many direct consequences of entropy
    and in a temporally localized way, entirely defeats it. (the entropy caused by the passage of energy through the biological system is
    'vented' into the outside world by the
    biological system.)

    ever wonder what urine and feces were?

    entropy in biological form, and it only
    gets better.... as uring and feces SERVE
    THE PERPETUATION OF THE BIOLOGICAL FORM.

    forget physics... too boring, too simple...

    ag.

    ReplyDelete
  22. Then again, without physics we would hardly have the amazing tools needed to study most of the other sciences. Or chemistry. And some chemical compounds were discovered through biology.

    Really, scientists should stop bickering. It's ALL interesting, but each one of us can only focus on so much- hence, specialization.

    ReplyDelete
  23. These are the best comments ever. You are all awesome nerds.

    ReplyDelete
  24. I'm interested in the implications for astrophysics. Are there stellar processes that generate these kinds of energy densities, and would they require significant coherence? In principle, it would seem like this could impact observations of distant cosmological objects, if the magnitude was significant. What effects would be important in this energy regime?

    ReplyDelete
  25. Internet win... rare, but does happen. I learned from the comments, and no 4chan or anything else screwing it up. Kudos.

    ReplyDelete
  26. SO this is how we get a light saber to work!! Incredible!!!

    ReplyDelete
  27. Geeks! (compensating for mental inadequacy)

    ReplyDelete
  28. Re. "forget physics... too boring, too simple...": http://xkcd.com/435/ I think that's all to say :P

    ReplyDelete
  29. Um, if candle burning counts as mass->light, then light->mass is also very commonplace, taking place in most photochemical reactions and even in plant growth.

    ReplyDelete
  30. http://xkcd.com/435 was exactly what came to my mind, when I started reading the post about biology :D

    ReplyDelete
  31. Here is one example of how photon-photon scattering might work: If the energy of a pair of photons is high enough there is a chance of each creating an electron/positron pair which can then further interact with each other before annihilating and creating new high energy photons. Total momentum is conserved during this process but these new photons can individually have different momenta.

    If you step back and squint, view the electron/positron creation as an intermediate process, what it looks like from the outside is that two photons just came in and scattered off of one another.

    The electromagnetic field alone doesn't interact with itself in the absence of charged matter. But if charged particles are present it self interaction becomes possible by way of the charges.

    As a word of warning I am a little rusty and haven't spent much time thinking about this so if something looks flawed it may, in fact, be.

    ReplyDelete
  32. Dear Biology Nerd

    Perhaps you don't get physics and thats why you find it boring. For example you believe life systems are above the laws of thermodynamics. Order, or the opposite of entropy, requires energy (food) to be increased. By takeing energy from some where you are creating entropy. The entropy of the universe always increases. By looking at biology in isolation you ignore the framework in which life resides.

    ReplyDelete
  33. Matter from light in itself is a well-known phenomenon, namely in electron-positron pair production from an Xray photon (energy > 1MeV) in the electric field of a nucleus, see: http://en.wikipedia.org/wiki/Gamma_ray
    (Blackett 1933, Nobel Prize 1948)

    ReplyDelete
  34. > Anonymous said...
    > These are the best comments ever. You are all awesome nerds.

    That was the best comment of these awesome comments.

    ReplyDelete
  35. How come it takes 13 years before this is news..? What happened in the last 13 years with this research?

    ReplyDelete
  36. I wonder if the materials that have been used to create the laser itself would be a factor in this limitation, or perhaps the vacuum is not pulling all of the atmosphere out as it should. The photons have to be pulled from somewhere..

    ReplyDelete
  37. The lead paragraph claims that this places some kind of limit on the destructive potential of the Empire's Death Star, but I don't see it. The only limitation mentioned was on intensity. That would be energy per unit area. But there does not appear to be a limit on the size, as in beam width or diameter. So if a 1 meter wide laser beam can't reduce a planet to rubble, one can still seek to make a 10 meter wide beam, or 100 meters, or... So, does this research pose any limit on destructive capabilities of a laser weapon? It clearly limits the intensity at the focus, but that intensity still packs a wallop, and you are free to make the focus as large as you please.

    ReplyDelete
  38. Darth Vader will be glad about that, looking forward to installing it in a starship and using it.
    http://www.youtube.com/watch?v=9ScAHXN_kAY

    ReplyDelete
  39. Another monstrous twisting energy to propel the aerospace vehicles comprable with Bossonova monstous twisters of Tornado to tap out energy in wind mill blades.
    An intersting cross polarisation at the middle neutral domain an upward force generated may be used in space vehicles.
    Anonymous

    ReplyDelete
  40. Magnetic tornado that grows stronger
    Using the Swiss Spallation Neutron Source (SINQ), Prof. Bianchi and his team cooled a single-crystal sample of CeCoIn5 down to 50mK above absolute zero and applied a magnetic field nearly high enough to entirely suppress superconductivity. They found that the core of the vortices feature electronic spins that are partly aligned with the magnetic field.
    This is the first experimental evidence that a theory that describes the properties of superconducting vortices and, for which Abrikosov and Ginzburg received the Nobel Prize in 2003, which does not generally apply in magnetically-induced superconductors.
    "When subjected to intense magnetic fields, these materials produce a completely new type of magnetic tornado that grows stronger with increasing fields rather than weakening," said Prof. Bianchi. "The beauty of this compound is how we can experiment without breaking it."
    Superconductors hold great promise for technological applications that will change how modern civilization can store and transmit energy - arguably some of the most pressing challenges today. Other notable applications include superconducting digital filters for high-speed communications, more efficient and reliable generators and motors, and superconducting device applications in medical magnetic resonance imaging machines.
    The first superconductor was discovered nearly a hundred years ago, and in most materials this curious state with no resistance was shown to arise from the interaction of the electrons with the crystal; however, in this new material, superconductivity is thought to arise from magnetic interactions between electrons.
    The electron has a charge, but like a tiny magnet, it also has a magnetic moment called spin. In a singlet superconductor, the electron pairs are formed by electrons of opposite spin, which cancels the pair's magnetic moment. But when the material is placed in a strong magnetic field, the spins are forced to orient themselves along the field, as the field acts on each spin individually. Usually, this breaks the pairs and destroys superconductivity. The magnetic fields inside a magnetically ordered material tends to act in the same manner and thus that superconductivity and magnetism tend to avoid each other, although they are not always mutually exclusive.
    This discovery is extraordinary, since magnetic order exists exclusively when this sample is in the superconducting state. In this unique case, magnetism and superconductivity do not compete with each other. Instead, superconductivity generates magnetic order.

    ReplyDelete
  41. Hmmmmm, can't say I like the sound of that "cascade" effect. Eh, but scientists probably know what they're doing. Surely there will be no unforeseen consequences.

    ReplyDelete
  42. About the candle, mass is lost. It HAS to be, because of mass-energy conservation. If it didn't, you just created energy out of nothing, which isn't allowed.

    However, the amount lost is very very tiny, just looking at E=mc2 will tell you that much.

    And the guy who talked about biology doesn't actually seem to know what entropy is.

    ReplyDelete
  43. Of course the most illiterate comment here is from a biologist :P

    I was going to make a half-life joke but I think that's already been done. Nothing left to do but snark at our opposing force.

    ReplyDelete
  44. God says he's concerned about this. Can she have lasers on her tentacles?

    ReplyDelete
  45. is this the institude of technology?

    ReplyDelete