How well can a thermal superconductor protect against pulse lasers?

First off, what is a thermal superconductor? It is a material that has a theoretical infinite thermal conductivity, similar to what is displayed in near-zero helium-4. This practically means that heat can controlled to a degree previously unobtainable.

When it comes to lasers, this means that in theory no matter how intense the beam or the how tiny the spot size, as long as there is a mesh of thermal superconductors within the armor plating, the beam will only make the entire armor warm up instead of vaporising the portion it is shining on. At least until the armor reaches thermal capacity in which case the beam will start doing damage, but by then the wearer should have moved out of the way a long time ago.

Against a weaponized pulse laser however, I'm a bit skeptical. Such a laser weapon would heat dump enough energy into the surface that conduction does not take place, meaning that a mesh that was mentioned above would be useless against such a weapon.

In this true? Do Thermal Superconductors provide no protection from pulse lasers?

  • $\begingroup$ Do not mistake superconductivity to mean that it has infinite capacity. Superconductive wires, for example, stop being superconductive if you try and pass enough current through them. $\endgroup$
    – DKNguyen
    Nov 13 at 0:38

3 Answers 3


A laser will laugh at a thermal superconductor trying to stop it.

A thermal superconductor is very good at dissipating heat building up in a confined location, but a laser doesn't necessarily heat up the substance it hits.

A laser excites electronic or molecular transitions: only the molecular transitions result in direct heat, electronic transition result into the matter being ionized and all the shenanigans which later on result into heat.

By the time the thermal superconductor has started carrying away the heat, the laser has already done its damage.

  • $\begingroup$ It's the same reason why mirror armor wouldn't work. Once you hit really high intensities (like you would for a laser weapon), the electric field strengths are high enough to just rip electrons right out of atoms, bypassing the optical/material properties. $\endgroup$
    – BMF
    Nov 12 at 17:47
  • $\begingroup$ @BMF Basically how a Necron flaying beam works. $\endgroup$
    – DKNguyen
    Nov 13 at 0:41
  • $\begingroup$ oh wow, what would be useful against these laser weapon? $\endgroup$ Nov 13 at 3:25
  • $\begingroup$ @encryptoferia There is nothing known that would withstand a focused pulse with high energy. But there is a trivial solution where you put a lot of whatever, eg dust, in the way. This gets you good enough shielding; unfortunately happens naturally when you use lasers to work material. $\endgroup$ Nov 13 at 7:46
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    $\begingroup$ you'd need enough energy to ionise the atoms in the superconductor. That means you either need a high enough frequency that individual photons can eject bound electrons, or a high enough flux of photons that you get non-linear effects like multi-photon absorption (or even better, both!). If you don't meet either of those thresholds you'll only get electronic transitions if the frequency of the laser matches the absorption spectra of the elements in the superconductor. Definitely not an insurmountable problem, but still restrictive on possible weapons $\endgroup$
    – Tristan
    Nov 13 at 14:52

I've mentioned this subject briefly on various different occasions in one of my many, many laser cheerleading posts on this site passim ad nauseam. I'll gloss over the issue of high-temperature thermal superconductors here... they're unobtanium, in the sense of "we could establish plausible physical properties of this material, but it probably can't exist in real life". That category includes the stuff that holds wormholes open or makes Alcubierre warps possible, and so it is fair game for even reasonably hard scifi.

If your thermal superconductors somehow had infinite thermal conductivity, they'd resist purely thermal effects quite well, up to the capacity of your heatsinks and/or radiators. Obviously you could just cook a target by pouring more energy into it than it can dump, but that's probably not going to be generally practical... it should work on smaller targets, like missiles, but not very large things. With finite conductivity, you just have to deliver enough heat to a small enough space in a short enough period of time that the superconductor will vaporize before it can conduct it away, so a powerful enough heat source can defeat your armor.

The problem is that sufficiently intense laser light isn't just heat.

Short wavelength lasers, which mostly means vacuum UV and up (a 10 eV ionization energy corresponds to ~124 nm wavelength), ionize matter they illuminate and ionization is not a thermal effect. Your thermal superconductors, if they are made of matter, will not necessarily cope well with this sort of thing that can disrupt crystal structures and molecular composition and all sorts of things that superconductivity probably needs in order to work nicely.

Nuclear pumped lasers are one possible source of this sort of radiation, which implies a surprisingly low tech-level by the standards of having-warfare-in-space scifi... humans could probably make them now (project excalibur demonstrated the technique in 1980 as part of the guardian dauphin nuclear test) though they'd be quite expensive, I suspect. They're only pulsed by the nature of their pump source, so maybe they don't count, though. A free electron laser might also do the job... they already exist, though current examples are not at all suitable for weapons. You might reasonably find a way to shrink an accelerators right down whilst maintaining efficiency in a scifi setting, though that will be challenging in real life (wakefield accelerators are tiny, but very low efficiency making them poorly suited for weapons).

With sufficiently intense laser illumination, even using non-ionizing wavelengths, you can get nonlinear optical effects like multi-photon absorption which in turn can cause ionization if the total energy absorbed is sufficient (obviously this works better if the laser is short wavelength). Once those electrons have left the vicinity, the now positively-charged nuclei left behind will repel each other in an effect called a Coulomb explosion, and that's the end of your nice material structure and probably your thermal superconductivity, too.

Now, sufficiently intense is doing some heavy lifting there. From the wikipedia article on Coulomb explosions:

Coulomb explosions for industrial machining are made with ultra-short (picosecond or femtoseconds) laser pulses. ...enormous beam intensities [are] required (10–400 terawatt per square centimeter thresholds, depending on material)

That's a big ask, but not an impossible one.

This all means that if your thermal superconductor is made of matter, it cannot guarantee safety against laser weapons, though it will significantly reduce the effective range of lasers emitting non-ionizing wavelengths. It is unlikely to help much against VUV, x-ray or gamma-ray emitting weapons. You should also consider that the existence of thermal superconductors makes it easier to construct unreasonably powerful lasers.

If your tech-level precludes nuclear-pumped lasers and picosecond pulse generation, then thermal superconductors seem likely to render laser weapons significantly less useful.

  • $\begingroup$ Great answer! I would have chosen your answer if it weren't for the fact that I'm fairly certain that such I powered lasers don't function all that well in atmosphere. Which I should clarified, my bad. $\endgroup$
    – Seraphim
    Nov 14 at 7:29
  • $\begingroup$ @Seraphim not only does that completely change the question, but it isn't something that the accepted answer covers either... $\endgroup$ Nov 14 at 11:23
  • $\begingroup$ oh...I don't think changing this post will do much, so I'll make another one asking a similar question, but in atmosphere some time soon. $\endgroup$
    – Seraphim
    Nov 14 at 16:23

A "thermal superconductor" is not just a material with infinite thermal conductivity, they're not a direct analogue to electrical superconductors, as thermal conductivity isn't a direct analogue to electrical conductivity. For example, a consequence of electrical resistance is that energy is lost in the form of heat. Thermal resistance just results in a thermal gradient, heat isn't lost somehow in the process of flowing through the material.

In a thermal superconductor, changes in temperature propagate as a wave instead of by diffusion. This "second sound" is not particularly fast (around 20 m/s in the case of superfluid helium, increasing as temperature decreases), and the thermal conductivity is still finite. Additionally, at least in the case of helium-II, the heat capacity of the superfluid phase is much higher. They are very good thermal conductors, but you may be better off with a circulating liquid that can tolerate heating without drastically dropping in thermal conductivity and capacity.


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