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Will high power laser penetrate mirror?

  1. Jul 11, 2013 #1
    Many nations are developing hi-energy laser weapon. My question is, what if target is coated with mirror like coating? Can laser (since laser is still light) penetrate mirror? If it can then how is it possible?

    Regards
     
  2. jcsd
  3. Jul 11, 2013 #2
    Well mirror is just like any other material , the difference is that the coating of the mirror is of such material that has a very smooth surface and other characteristics that tend to reflect incoming EM radiation in the visible spectrum.In other words light.
    Now I am no mirror specialist but I do bet that nothing is pure so a mirror too absorbs some of the light (radiation) that's coming in it's way so with time it could heat up and break or other problems could arise.
    I'm sure others will comment more on this.
    I think key factors here are the wavelength of the laser light and the intensity.
     
  4. Jul 11, 2013 #3

    davenn

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    the trick around most of that problem would be to have the reflective surface on the front of the glass, as is done with telescope mirrors. That way the laser isnt passing through the glass

    Dave
     
  5. Jul 11, 2013 #4
    Yes I could agree but the material which reflects also absorbs something or are there materials that reflect 100% of some wavelength light? Although I don't think so.
     
  6. Jul 11, 2013 #5
    You are correct. There are no perfectly reflective materials. If the reflector is 99% efficient then the laser trying to penetrate it has to be powerful enough that 1% of it's energy will have the desired effect on the target. 1 big reason that this is technically difficult is that the laser itself absorbs some of its own energy so you wind up with as much destructive energy (heat) being produced within the weapon as you are delivering to the target. Add to that the fact that the beam will diverge between the weapon and the target so the energy will be more concentrated (destructive) at the weapon end of the beam.
     
  7. Jul 11, 2013 #6
    + add the efficiency of a typical even the best laser, and you get everything but not a weapon of choice.Despite all the fantasy movies and all the pretty red glowing stuff that people like so much.
     
  8. Jul 11, 2013 #7
    I use a laser cutter that cuts through silvered acrylic, I think it is an infra red laser, 30mW.
     
  9. Jul 11, 2013 #8
    Silver is only some 98-99% reflective for infrared, and less at lower wavelengths. The mirror will heat up and eventually burn off. If it's a thin mirror, it won't take much heat before failing.

    On the other hand, you can use thin films to increase reflectivity higher than 99%, but the thin films are even more easily destroyed.
     
  10. Jul 11, 2013 #9

    Bobbywhy

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  11. Jul 13, 2013 #10

    Claude Bile

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    No material is perfectly conducting and so there will always be some penetration of the laser field into the reflecting medium.

    For mirrors that are more than ~100 nm thick, the limiting factor to power reflectivity will likely be thermal damage due to absorption.

    Claude.
     
  12. Jul 13, 2013 #11
    During the cold war there was much discussion about putting high powered lasers in orbit in order to shoot down incoming missiles. The problem is that high powered lasers are massive and not easily aimed. The solution was to use mirrors to aim the laser but that put a limit on the maximum reflectivity of the missile. At some point the aiming mirror would melt before the missile.
     
  13. Jul 13, 2013 #12

    Bobbywhy

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    Surprise! This new discovery shows that some materials reflect 100% of the incident light!

    "Perfect mirror debuts
    Material that reflects light without letting any escape could improve lasers

    Physicist Chia Wei Hsu and colleagues at MIT weren’t looking to invent a mirror when they were studying the behavior of light interacting with a photonic crystal, a slab of material with a network of drilled holes, each so small that it can manipulate individual light waves. Most of the time, light penetrated at least partially into the team’s crystal, a block of perforated silicon nitride. But when the researchers shined a specific frequency of red light at a 35-degree angle to the surface of the slab, they were surprised to find that it bounced back completely — none of it leaked away or got absorbed."
    http://www.sciencenews.org/view/generic/id/351485/description/Perfect_mirror_debuts
     
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