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As I'm sure many of you educated folks on this stack exchange know, copper is one of the most heat-conductive common metals out there. My question: if, for some reason a society with early 20th century tech discovered laser weaponry (think lasguns from WH40K), would copper armor (perhaps ribbed or corrugated in some fashion to increase surface area and thus disperse heat energy more efficiently) be a feasible armor to equip relatively large amounts of infantry with?

For the purposes of this question, I'm not interested in the logistics or economics of such an undertaking, only the effectiveness of copper armor against laser weaponry. If not, better alternatives would be welcome.

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    $\begingroup$ I wonder if your armor could be made out of high quality mirrors? $\endgroup$ Mar 26 at 11:28
  • $\begingroup$ I did consider mirrors, but in a battlefield environment, I figured mirrors might get cracked easily, producing chips and shards that would be more harmful to the wearer than protective. Maybe mirrors could be used on aircraft as protection/camouflage, but on infantry, where men are running about, crouching and lying prone on rough fields strewn with rocks and rubble? $\endgroup$
    – KaiGuyMBK
    Mar 27 at 1:43
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There's a bit of a problem in how you define "laser weaponry".

To my mind, modern industrial laser hardware really isn't comparable to laser weaponry, because the peak powers are generally just too low. Unless each pulse of your laser is delivering a few tens of joules in no more than a couple of microseconds (and hence your laser is, at a minimum, developing peak powers in the megawatts) then what you've got isn't really very useful as a weapon, and will compare extremely poorly against any other kind of weapon, including railguns, coilguns, guided missiles, unguided rockets and plain old chemically-driven guns.

Once you've created a laser capable of this sort of performance, the thermal conductivity of the target is more or less irrelevant because there's insufficient time for the heat to be conducted away before the material has been evaporated. At that point what you need is an armour that is tough and refractory, and copper is neither. Conventional steel armour plate is much more practical in the face of that sort of weapon, because its melting point is much higher as is its heat of vapourisation and even its specific heat capacity and its a hell of a lot tougher to boot. That means that practical lasers will make shallower, narrower holes in steel armour than they would in copper but perhaps more importantly it protects against conventional weapons too.

If your enemies are using lasers that can be effectively defended against simply by wearing copper plate armour, then your enemies are poorly-equipped idiots and you should thoroughly teach them the folly of their ways using plain old bullets, bombs and shells. Bonus points if you can trick them into wearing copper armour to defend against lasers, which ends up being a logistical and economic nightmare and fairly ineffective against decent guns.

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  • $\begingroup$ Thanks! Very useful info, and very digestible for a man uneducated in the sciences such as myself. $\endgroup$
    – KaiGuyMBK
    Mar 26 at 11:03
  • $\begingroup$ @KaiGuyMBK no problem. If you ever need Grumpy Opinions about lasers and laser defenses, I have so many that I'm always happy to share ;-) $\endgroup$ Mar 26 at 11:07
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No, copper won't be a feasible armor against laser.

As you can see from this paper, aptly titled Ultrafast laser ablation of copper by GHz bursts, copper can be ablated by a laser.

the ablation performance can be maximized by properly selecting the pulse number, separation time, and energy in a laser burst. The numerical result shows that the present prediction is in fairly agreement with existing experimental result. Under the same total laser fluence of 32 J/cm2, a 10 GHz burst laser with an optimized 128 sub-pulse can significantly enhance the ablation depth, 4.2 times that a single pulse does. It is found that the optimized ablation depth is a linear function of the total fluence of ultrafast laser bursts.

In particular the part stating

ablation performance can be maximized by properly selecting the pulse number, separation time, and energy in a laser burst

tells you that it just a matter of playing some knobs to optimize the damages done by the laser.

This other paper also supports that view

Ultrashort pulse laser, capable of varying pulse duration between 210 fs and 10 ps and producing a burst of pulses with an intra-burst pulse repetition rate of 64.5 MHz (time distance between pulses 15.5 ns), was used to investigate the ablation efficiency of the copper. The study on ablation efficiency was done for various numbers of pulses per burst between 1 and 40. The increase in the ablation efficiency by 20% for 3 pulses per burst compared to a non-burst regime was observed. The comparison was made between the beam-size optimised regimes. Therefore, the real advantage of the burst regime was demonstrated. To the best of our knowledge, we report the highest laser milling ablation efficiency of copper of 4.84 µm3/µJ by ultrashort pulses at ~1 µm optical wavelength.

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  • $\begingroup$ I can't find any papers that have an ablation of Cu of more than 1mm. Generally, laser ablation of any depth is difficult without techniques such as trappaning. Infantry wearing this kind of armour would likely be in motion making such a technique difficult - especially if the laser is also hand held. $\endgroup$
    – Hukk2010
    Mar 26 at 9:07
  • $\begingroup$ @Hukk2010, I see here that cutting 1 mm is feasible with 1000 W power. I assume military wouldn't go mild there $\endgroup$
    – L.Dutch
    Mar 26 at 9:11
  • $\begingroup$ That is a CO2 laser, not an ultrashort pulse laser as described above. Longer pauses between pulses allow sloped sides to form in the material walls (decreasing the fluence) and plumes to dissipate the incoming beam. However, this is a question about armour rather than weaponry. Copper would provide some protection for a moving infantryman but it wouldn't render them impervious. $\endgroup$
    – Hukk2010
    Mar 28 at 11:16

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