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Frickin’ Laser Beams: Fact vs Fiction

54 points by J3L2404 16y ago

rflrob 16y ago
>But really, the most likely place for lasers as a viable weapon is space. Without air, the difficulties with plasma creation and turbulence are removed. The issue of power and optics remain, but I could plausibly see a satellite or space station with the stability and power to use a laser as a weapon. The hard part of almost any space-based power consumption is the difficulty of later dissipating the wasted heat energy. Conduction and convection don't work when there's no surrounding medium. Without lots of clever technology, then, your space-based laser is a double-edged sword.
- electromagnetic 16y ago
  > The hard part of almost any space-based power consumption is the difficulty of later dissipating the wasted heat energy. ... Without lots of clever technology, then, your space-based laser is a double-edged sword. Not if you design it like a mine or a one-shot munition. Cheap high-powered lasers and targeting systems will pave the way for laser-mines in space. Without air, there is little need to pulse your lasers. Your weapon might as well expend itself ASAP to do maximum damage without prolonged tracking and risk of retaliatory fire. If you can only sustain pulsed fire at say 6 shots per minute, that gives your enemy a lot of time to triangulate and return fire, potentially with more lasers than you have. However, you could simply expend your munition by firing it continuously for a minute until your mine overheats and its systems fail. If you're lucky your mine might survive the battle through a bad retaliatory shot, or by destroying the target. If your mine survives, it could well live to fight another day. It will eventually cool down, and assuming you'd provide it with solar panels it could well charge itself up to repeat the process next time you're attacked. It's also nice to point out that smaller objects dissipate their heat faster, so attaching your weapons inside your ship may only serve to hamper your efforts to fight effectively. If you're actually defending something, like say a asteroid mine then you're likely to have enough spare material to afford heat sinks, or you could use several meter wide asteroids to mount your lasers. Drill tubes and heat-sink into the asteroid (it doesn't matter what it's made of, but a metallic asteroid would be ideal) with copper-rods and you could fire for even longer periods. On top of this, you could use the asteroid as a heat-sink for the enemy fire. If you know a ship-mounted laser only fires once every 10 seconds, you could simply realign so that there's a high probability that your enemy will be hitting rock and not a vital system. I doubt we'll be using them any time soon, but I think what people fail to understand is the incredible vastness of space, but also the potentially endless resources we will find there (at least from our present perspective where we can't strip-mine our planet because of all that inconvenient molten-gooiness that is containing precious materials).
eof 16y ago
> The air poses another problem: it absorbs light. In fact, a high enough powered laser can cause the air itself to break down into a ragged line of plasma. I’ve seen this in the lab and it is awesome. Badass. edit: http://www.youtube.com/watch?v=ZeqIZyUMDP4 http://www.youtube.com/watch?v=ZeqIZyUMDP4
- quanticle 16y ago
  I mentioned lightning earlier and that’s relevant here. There is a way to make use of the “plasma issue”, because plasmas conduct electricity. So in theory it would be possible to use a laser as a long-distance taser! The laser would first create a conduit of plasma out of the air, and then with a high enough voltage, an electric shock could be send down the plasma to the target. This would not be a subtle weapon: at this point the lightning analogy is not really an analogy anymore. It would basically be a lightning gun, and would make a noise to match. I thought I was being really clever when I thought of this, but it turns out I’m not the first: the US military has experimented with them. So we don't get lasers but we do get plasma cannon/particle beams/PPCs? I'm okay with that.
  - khafra 16y ago
    I've thought about making a lightning gun that way, before. Unfortunately, a CO2 laser powerful enough to cause dielectric breakdown of air over a useable distance is inconvenient to carry; and then making sure the electricity gets grounded through the target instead of the gun's wielder is tricky too.
  - nolite 16y ago
    Hmmm... so controlled dielectric breakdown with lasers... Use E-fields from lightning to produce gamma rays via http://www.wired.com/wiredscience/2011/01/lightning-antimatter-physics/ http://www.wired.com/wiredscience/2011/01/lightning-antimatt... collect positrons with a magnetic bottle. Finish with big jars of antimatter. I wonder...
IgorPartola 16y ago
One myth left: can I just use a mirror to reflect the high power laser at the gun that fired it to destroy it?
- ramidarigaz 16y ago
  I imagine that a laser powerful enough to destroy itself would have no problem with a mirror.
- mechanical_fish 16y ago
  Mirrors are not 100% efficient. That fraction of one percent will kill you if the incident power density is high enough. Once one little portion of the mirror is absorbing more energy than it can dissipate, that portion will heat up and up. When it gets hot enough it tends to become less reflective - it oxidizes or maybe just evaporates - and then you've got even higher absorption at that spot, which makes it fail even faster and helps heat up adjacent spots... When this happens with a pulsed laser you can sometimes hear it. That tiny snap-snap-snap is the sound of your three-hundred-dollar optic heading for the trash. You'll look at it and see the telltale little spots. If you're cheap you'll try just sliding it sideways to a non-spotted bit of surface, but sometimes there isn't enough mirror for that... That's with a high-tech custom-designed laser mirror, not a random surface of some random object. And we're generally not trying to destroy it. And yet they often get destroyed, when you screw around with high-intensity lasers.

54 points by J3L2404 16y ago

>But really, the most likely place for lasers as a viable weapon is space. Without air, the difficulties with plasma creation and turbulence are removed. The issue of power and optics remain, but I could plausibly see a satellite or space station with the stability and power to use a laser as a weapon. The hard part of almost any space-based power consumption is the difficulty of later dissipating the wasted heat energy. Conduction and convection don't work when there's no surrounding medium. Without lots of clever technology, then, your space-based laser is a double-edged sword.

electromagnetic 16y ago
> The hard part of almost any space-based power consumption is the difficulty of later dissipating the wasted heat energy. ... Without lots of clever technology, then, your space-based laser is a double-edged sword. Not if you design it like a mine or a one-shot munition. Cheap high-powered lasers and targeting systems will pave the way for laser-mines in space. Without air, there is little need to pulse your lasers. Your weapon might as well expend itself ASAP to do maximum damage without prolonged tracking and risk of retaliatory fire. If you can only sustain pulsed fire at say 6 shots per minute, that gives your enemy a lot of time to triangulate and return fire, potentially with more lasers than you have. However, you could simply expend your munition by firing it continuously for a minute until your mine overheats and its systems fail. If you're lucky your mine might survive the battle through a bad retaliatory shot, or by destroying the target. If your mine survives, it could well live to fight another day. It will eventually cool down, and assuming you'd provide it with solar panels it could well charge itself up to repeat the process next time you're attacked. It's also nice to point out that smaller objects dissipate their heat faster, so attaching your weapons inside your ship may only serve to hamper your efforts to fight effectively. If you're actually defending something, like say a asteroid mine then you're likely to have enough spare material to afford heat sinks, or you could use several meter wide asteroids to mount your lasers. Drill tubes and heat-sink into the asteroid (it doesn't matter what it's made of, but a metallic asteroid would be ideal) with copper-rods and you could fire for even longer periods. On top of this, you could use the asteroid as a heat-sink for the enemy fire. If you know a ship-mounted laser only fires once every 10 seconds, you could simply realign so that there's a high probability that your enemy will be hitting rock and not a vital system. I doubt we'll be using them any time soon, but I think what people fail to understand is the incredible vastness of space, but also the potentially endless resources we will find there (at least from our present perspective where we can't strip-mine our planet because of all that inconvenient molten-gooiness that is containing precious materials).

eof 16y ago

> The air poses another problem: it absorbs light. In fact, a high enough powered laser can cause the air itself to break down into a ragged line of plasma. I’ve seen this in the lab and it is awesome. Badass. edit: http://www.youtube.com/watch?v=ZeqIZyUMDP4 http://www.youtube.com/watch?v=ZeqIZyUMDP4

quanticle 16y ago
I mentioned lightning earlier and that’s relevant here. There is a way to make use of the “plasma issue”, because plasmas conduct electricity. So in theory it would be possible to use a laser as a long-distance taser! The laser would first create a conduit of plasma out of the air, and then with a high enough voltage, an electric shock could be send down the plasma to the target. This would not be a subtle weapon: at this point the lightning analogy is not really an analogy anymore. It would basically be a lightning gun, and would make a noise to match. I thought I was being really clever when I thought of this, but it turns out I’m not the first: the US military has experimented with them. So we don't get lasers but we do get plasma cannon/particle beams/PPCs? I'm okay with that.
- khafra 16y ago
  I've thought about making a lightning gun that way, before. Unfortunately, a CO2 laser powerful enough to cause dielectric breakdown of air over a useable distance is inconvenient to carry; and then making sure the electricity gets grounded through the target instead of the gun's wielder is tricky too.
- nolite 16y ago
  Hmmm... so controlled dielectric breakdown with lasers... Use E-fields from lightning to produce gamma rays via http://www.wired.com/wiredscience/2011/01/lightning-antimatter-physics/ http://www.wired.com/wiredscience/2011/01/lightning-antimatt... collect positrons with a magnetic bottle. Finish with big jars of antimatter. I wonder...

IgorPartola 16y ago

One myth left: can I just use a mirror to reflect the high power laser at the gun that fired it to destroy it?

ramidarigaz 16y ago
I imagine that a laser powerful enough to destroy itself would have no problem with a mirror.
mechanical_fish 16y ago
Mirrors are not 100% efficient. That fraction of one percent will kill you if the incident power density is high enough. Once one little portion of the mirror is absorbing more energy than it can dissipate, that portion will heat up and up. When it gets hot enough it tends to become less reflective - it oxidizes or maybe just evaporates - and then you've got even higher absorption at that spot, which makes it fail even faster and helps heat up adjacent spots... When this happens with a pulsed laser you can sometimes hear it. That tiny snap-snap-snap is the sound of your three-hundred-dollar optic heading for the trash. You'll look at it and see the telltale little spots. If you're cheap you'll try just sliding it sideways to a non-spotted bit of surface, but sometimes there isn't enough mirror for that... That's with a high-tech custom-designed laser mirror, not a random surface of some random object. And we're generally not trying to destroy it. And yet they often get destroyed, when you screw around with high-intensity lasers.