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  • Context:

It is a military sci-fi story where they use technologies that are expensive today because they already became common place. For example, laser-induced-graphene supercapacitors, carbon nanotube artificial muscles etc.

I was thinking on using these LIG (laser induced graphene) supercapacitors to power solid state lasers, such as synthetic ruby rod lasers because they seem pretty simple and straight forward (at least for me). But if you have better solid state lasers in mind, I wouldn't complain.

You don't need to worry about the supercapacitors, batteries or whatever to answer the question.

I was thinking for this solid state ruby laser to be used by the 2 meter tall carbon nanotube artificial muscles small mechs from the infantry, or an armored vehicle. But again, not essential for the question.


  • The Solid State Ruby Laser:

As I could see, the solid state ruby lasers just need a flashtube to work (and other details aswell).

So, the idea would be to put one or more rods surrouned by a lot of medium lamp-like flashtubes inside a chamber, so they could emit more intense light without the risk of exploding. But of course, it could depend on how much energy the ruby rod would be able to take before simply melting from the amount of energy.

I was thinking of a meter long ruby rod with a diameter of 5 cm surrounded by 8 lines consisting of 21 flashtubes (totalling 168 flashtubes), every flash tube would have a diameter of 4.5 cm inside a reflective chamber.


  • The Question:

I think it would be easier to calculate using materials that already exist, such as conventional body armor or just meaty bodies from animals (or humans).

How much energy should these flashtubes receive to emit a pulsed laser strong enough to cause a serious enough damage equivalent to kill a human at maximum distance of 300 yards in less than a second? (using lenses to focus the beam, if you so decide to use them on your answer)

("in less than a second" because even a normal engraver laser could kill a human... If you gave them burns all through their body over a couple of hours)

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    $\begingroup$ You've got two questions here -- how much pulse energy is needed to emulate a bullet, and how much energy will the tubes/rods/diodes have to receive to produce that pulse. Please try to ask one question per question (hint, the laser efficiency question is probably easy to research). $\endgroup$
    – Zeiss Ikon
    Oct 4, 2022 at 16:04
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    $\begingroup$ @ZeissIkon fixed it (I think). I assumed that since since the only way the laser can work is through the flashtubes, there wouldn't be too much of a difference on powering what... $\endgroup$
    – Fulano
    Oct 4, 2022 at 16:11
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    $\begingroup$ That's a very wrong assumption. A ruby laser takes more than 1000x the energy in as it puts out; the rest goes to heat (in the flash tubes and the rod and a little in other losses). And you're still asking how much input to match a rifle bullet -- how much output is more of a worldbuilding question, since the efficiency of ruby lasers is well known and hasn't changed in decades. Also, I doubt you'll get a hard science answer on the rifle bullet equivalence. Might want to swap that tag for "science-based" instead. $\endgroup$
    – Zeiss Ikon
    Oct 4, 2022 at 16:39
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    $\begingroup$ BTW, I no longer think this is a worldbuilding question. You're not asking about the rules of your world. You're asking (quite literally) about how to write your story. Think about it this way: "How do I power my laser?" is a worldbuilding question that can be answered, "with supercapacitors" based on our application-of-tech policy. Compare this to "how many supercapacitors do I need?" the answer to that question is VTC:Too Story-Based because it's really just an aesthetic of your story, not a rule of your world. It depends too much on other aspects of your story. $\endgroup$
    – JBH
    Oct 5, 2022 at 16:51
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    $\begingroup$ To summarize: Pick a number that sounds good for the purpose of your story and move on. Nobody is going to pick apart your explanation of how your laser works (if you explain it at all) just to see if your choice of number is scientifically-accurate. I believe you've been caught by a common worldbuilding problem: you're trying to be too precise. The rabbit hole of precision and detail is very, very deep and the deeper you go the less valuable the details are to your worldbuilding efforts. $\endgroup$
    – JBH
    Oct 5, 2022 at 16:54

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I think that the question you're actually asking is "how powerful would a laser have to be in order to emulate the effect of a .22 long round at 300 meters." Let's do a bit of back-of-the-napkin math.

There are a huge number of obstacles to answering this question. A quick google tells me that your typical .22 long round has around 162 joules of energy. You might THINK that most of that energy passes through a person, but if there were spare energy, they would put less powder in the charge. This is roughly the power required to reliably penetrate a lightly armored body.

If you want to have roughly the same effect from a laser, you'd pretty much have to explosively boil a chunk of the person's body. If you're thinking you can just burn a hole through them, then let's call that a 1 cm hole through about 12 cm of body. Just to simplify the math, let's call that 10 cubic centimeters.

It takes somewhere around 330 joules to heat 1 cc of water from room temperature to boiling, so you'd have to deal a tightly focused 3300 joules of energy to a bare chest to make this happen. If they're wearing armor, then you have to vaporize the armor first, and that's a MUCH higher number, even assuming that the armor isn't reflective. Conveniently, 1 joule == 1 watt, so you're looking at 3300 watts of laser out of the business end.

How much energy has to go into that? I found this page: https://www.tandfonline.com/doi/abs/10.1080/03772063.1970.11486671

Which tells me that best efficiency you're going to get for a ruby laser is around 23.7%, so you're going to have to pour at least 14kw into your ruby to get the effect you're looking for, and you'd be shedding three times the heat you hit the person with out of your gun, so you better have some significant heat sinks.

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