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Comment by chris_va | Hacker News Reader

My read is that this will be great for commercial applications (e.g. welding, lighting), but a weapon that doesn't work in a smokey/foggy environment is going to be fairly easy to circumvent. Environments where something is being hit with a high power laser tend to end up being smokey/foggy.

That won't make it useless, but it will definitely reduce utility and adoption. 100kW really is not that much, unless you can focus it to a fairly small diameter, which just is not possible at long distances.

My personal favorite for a "ray gun", and far more difficult to make work, is the Laser-Induced Plasma Channel.

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I think this is more a point defence (aa) weapon you could imagine one mounted in a second turret on a MBT to counter missiles / rpg's

It would also if equipped with image recognition help protect the tank against enemy infantry - might not be to popular with you own grunts though.

Probably okay for targetted drone assassinations though

Tinfoil hats, back in style.

Is targeted drone warfare still a tinfoil hat topic? I read I don’t know how many articles about Bush and Obama expanding a targeted drone program and the public seems to have just kinda shrugged.

Edit: dead comment below points out I might be missing a joke: tinfoil is for blocking the lasers. D’oh

No tinfoil necessary when it's a well-documented fact.

https://www.independent.co.uk/news/world/americas/donald-tru...

Would the laser not burn a passage through any particulates, yes it would intialy attenuate tbe beam, but would then burn through

Wouldn't that depend heavily on the reflectivity of the particles?

Also depends on whether particles are being freshly generated by the target. An aircraft could "smoke" itself - i.e. emit a particulate cloud from a grid of pores in its skin - in response to being targeted or fired upon by directed energy weapons.

Also isn't it trivial to reflect the laser back to its origin? And if the laser is powerful enough to take down a missile, I'd thought the reflection of the beam on smoke may be harmful to humans too.

Reflect it away perhaps, back to origin would require a lot of control or luck. The other thing to keep in mind is that a "reflective" surface is not a perfect reflector so some energy transfer will occur and if that transfer damages the reflective surface it leads to more energy transfer, etc.

The exterior of a potential target could be covered in corner reflectors[1]. Such a surface reflects most of the light directly back to its source.

Corner reflecting is the reason vehicle reflectors appear so bright under illumination.

I wonder how good such a counter measure would be?

[1] https://en.m.wikipedia.org/wiki/Corner_reflector

It will be hard to hit the gun itself but what about reflecting it to the ship carrying the gun?

Reflecting the ray in the general direction of the laser, yes.

Reflecting it so that it could do any damage, hardly. You'd have to have a high-precision reflector to keep the reflected beam narrow, especially at a long distance. The reflection will likely have an order of magnitude larger area, and thus lower power density. A ship firing the laser is likely much sturdier and more massive than a missile it tries to gun down with the laser beam.

Also, I get from Ian Banks' SF, mirrors are a defense. And indeed, blowback offense.

Mirror shields in the Culture series use the 'field' magic that so much of the Culture's science relies on. Presumably a reflector field is both insanely reflective (99.999% or better, like dielectric mirrors) and resilient to the air the field's being projected in heating up massively from the small energy fraction which is absorbed.

Your typical "glass with metal on it" mirror will fare very poorly against a high power laser. They're only ~90% reflective, and 10% of a high power beam is more than enough to turn your mirror into a 0% reflective smoldering black lump.

Even if you build a mirror with very high reflecting factor in the wavelength of your enemy's weapon, all it takes is a smudge of dust or oil on the surface and the thing is toast.

True. But on the other hand, there are mirrors in the laser itself that don't end up as toast. And in some circumstances, I can imagine throwaway mirrors that would reflect back substantial power before destruction. More or less a variant on chaff.

  there are mirrors in the laser itself that
  don't end up as toast.

Someone showed an industrial laser cutter to me once. He told me that:

1. The internal mirrors were about 5cm diameter, and water cooled.

2. The laser is only brought fully into focus at the final lens, just before the cutting point. So the beam at the mirror might have a 2cm diameter, before being focused down to a 0.5mm diameter at the cutting point.

Point 2 was also a key part of the safety system; the safety barriers could actually be quite thin, as the laser would be out of focus at that distance no matter how far wrong the optics went :)

If memory serves Traveller (game) mentioned aereosols (like smoke grenades) to counter lasers.

"Sandcasters". And in some incarnations of the game the clouds they produced would even be actively manoeuvred through space by some absurdly improbable application of magnetic force, to make defense an active skill (vs mindlessly pumping "more energy to shields")

Sandcasters were used for space combat. I am away from my library so I cannot check but I seem to remember smoke/aereosols to be used for ground combat to reduce laser effectiveness.

What we really need is an energetically advantageous way to produce high energy neutral particle beams. That would start to look more like the ray guns of science fiction than lasers ever will. It’s not just the weather either, when you hit a target that has a bit of appropriate ablative armor, you’ll be dealing with another source of bloom.

LIPC tech is good too, and might be closer than you’d think. You can exploit the interaction of ultrashort laser pulses to create and modulate plasma, and then do neat things like send a bunch of volts down the channel.

Something like a Godiva device (pulsed nuclear reactor)?

https://en.wikipedia.org/wiki/Godiva_device

They have a risk of creating a small nuclear explosion though.

Or just use the plasma directly - https://youtu.be/ML79u9zPZu4?t=2m47s

Lightning!

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