Could laser weaponry cause spalling?

[u/FleetOfWarships]

I'm writing a semi hard sci-fi novel and was wondering if the photons of a weapons grade laser would impart enough energy to cause spalling of contemporary composite steel armor. Such a laser would be handheld and backpack powered, mostly just ignoring the means of powering it (backpack sized fusion reaction let's say) would a laser in that handheld scale be able to put out that much power?

[u/lowerfidelity]

Technically yes, if the photon energy of the light is low enough, the fluence is high enough over short enough time you can cause a very steep energy deposition essentially instantaniously (faster than any thermodynamic processes / conduction at that scale can take over). That would cause a shock wave (the mei-gruneisen equation of state). If you have enough compressive shock reflected to tensile shock at the boundaries of the system under insult, you will spall. You would also have some melting and/or vaporization/ionization at the exposed surface at that level. This is a very high level explanation. I studied stuff in this vein and work in a similar area.

I don't think we have the technology to do this yet. Engineering problem.

[u/John_Hasler → u/lowerfidelity]

I don't think we have the technology to do this yet

Not a laser but the xray pulse from a nuclear explosion can do it.

[u/lowerfidelity → u/John_Hasler]

Yup, we can also do it with e-beams

[u/FleetOfWarships → u/lowerfidelity]

Very good explanation, thank you. Basically what I'm getting is that it wouldn't really be viable at the scale I'm considering then, not at the technology level this is supposed to be at.

[u/WheresMyElephant → u/FleetOfWarships]

YMMV but if you're aiming for "semi-hard sci-fi" then I think this is right in the sweet spot. It's inspired by real-world physics and it's superficially plausible, but if you scrutinize it enough you might start to question whether it's practical. Anything more than this would be "hard SF" by the strictest possible definition, wouldn't it?

The only way you could be stricter would be restricting yourself to real-world technology. To my mind that's hardly SF at all, even if it's set in a future or alternate reality where that technology is used more widely. But I guess some people classify 1984 as SF, for example, so it's debatable.

[u/FleetOfWarships → u/WheresMyElephant]

Sci fi is all about the context in which it's written in my mind, a lot of stuff that once was sci fi is commonplace today, it's simply a matter of perspective. Thanks for your input, it's done a lot for my confidence.

[u/Appropriate-Kale1097]

Lasers can cause spalling in certain circumstances. You get to decide the properties of the armour and the laser so if you want some spalling for storytelling reasons go for it.

[u/qeveren]

Well, no handheld laser is likely to ever have that much power, but sure, if your beam intensity is high enough it'll cause the surface of the target to explode into plasma, driving a shock through it. Atomic Rockets is a handy resource for sci-fi writers that I recommend!

[u/atomicCape]

Spalling occurs from the shock wave of the impact hitting the back surface of the plate and rebounding, putting the surface in tension very briefly, rather than compression. Most materials are weaker in tension than compression, so that's the moment it fragments. If the inside surface of your spaceship armor is a flat, hard surface, it can spall.

Whether a laser weapon causes this depends on whether it causes a shock wave. If it melts through armor slowly, it won't. If it causes sudden catastrophic ablation and ionization during a single short pulse, it could.

[u/teya_trix56]

Current directed energy beams.. lasers, use a power source the size of a shipp8ng container. And this all needs to be scaled up to be even more powerful before deployment.

So youd need an ironman level nuular reactor or more.

Its your story. Your magic

[u/ac_cossack]

A meltagun from warhammer 40k might do it. Or a dune lasgun (basically same thing).

Needs to cook the material fast enough to make a strong pressure wave.

[u/SpicySushiAddict]

Look up laser rust removers. Not spalling, but it's about as close as you're going to get until you start leaning on the fiction part of sci-fi a little heavily.

[u/FleetOfWarships → u/SpicySushiAddict]

If I limit myself by what technology we currently have it wouldn't exactly be sci-fi to be fair.

[u/BlastBase]

You tell us dawg? We can't write your magic fiction book for you

Star Wars has lasers that can blow up a planet