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This is not really connected to my story but I had an idea of having finger guns that actually work. Because lasers are cool I thought that you could have a character with the ability to magically generate lasers from their fingertips. Let's say that they could generate a laser with a high amount of wattage from their finger tip. Also, let's assume that this laser is near infrared since I think that is the absorption frequency of human skin.

Would it be effective for combat against an armed person or would it not be effective in combat due to constraints like distance or speed of a kill?

Edit: Would a pulsed laser of a high wattage with a fast/shorter pulse length be a good alternative to a cw laser of high wattage? And what if the spot size was that of let’s say 0.1 millimeters would it change the lethality.

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    $\begingroup$ Is there a reason why it has to be 100W or anything else? It's magic, you can just pick a bundle of desired effects and work backwards from there towards numbers if necessary to make sure they're approximately consistent with each other (if consistency is even desired - Superman being able to lift trucks one handed, but only knock out bank robbers when he punches them, is a feature, not a bug). $\endgroup$
    – g s
    Commented Apr 26 at 14:37
  • $\begingroup$ Just edited the question $\endgroup$ Commented Apr 26 at 15:50
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    $\begingroup$ Not sure how it's a gun at that point. It's practically magic, which you literally said in your question. Which is fine. Just it becomes: Finger lasers. Also we need some more context and limitations. Otherwise why not generate a beam like that of a space ship in a science fiction story. Lack of limitations and proper context actually makes it harder to provide a useful answer. $\endgroup$
    – Seallussus
    Commented Apr 26 at 16:29
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    $\begingroup$ 100 Watts are not much for a combat, but I assume the lasers are strong enough to cause eye damage, so targeting the eyes would permanently blind the victims. $\endgroup$ Commented Apr 26 at 16:38
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    $\begingroup$ Just to clarify, Watt is a measure of power, whereas Joule is a measure of energy. It makes a huge difference. 100 Watts for a nanosecond is nothing much, 100 Joules delivered in a nanosecond is lots and lots of energy. $\endgroup$ Commented Apr 26 at 16:51

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I think the issue here is the important difference between power and energy.

100 W is not really very much power. A 100 W CW laser delivers 100 joules of energy over 1 second. That's not a lot of energy. A 9mm bullet might deliver 400-800J of energy to the target at close range in less than a millisecond, and if you aren't delivering more energy than a 9mm then you may as well not bother. Once a bullet has hit you, it has done its job. Once your laserbeam has hit someone, you have to keep it on the exact spot in order to maximize damage... if the target moves (which they will!) you end up burning a stripe over them. Unless you hit something very delicate (like an eye) or your target is immobilized, you're going to be causing some fairly nasty burns but it'll take an unpleasantly long time to actually kill someone that way.

Would a pulsed laser of 100 watts and 1 nanosecond be a good alternative to a cw laser of 100 watts?

A pulsed laser that can deliver 100 joules per 1 nanosecond pulse has a peak power of 100 GW. A pulsed laser that has a peak power of 100 W delivers 100 nanojoules in that pulse.

The former is potentially extremely dangerous. The latter is extremely not.

Fully detailing the mechanics behind pulse lasers, or why you'd want a pulse laser rather than a CW laser for a weapon is a bit out of scope for this question, and likely to take up rather a lot of room. I recommend having a read of Project Rho's take on the matter (or at least, the takes that the author has collated). On CW lasers, they are referred to as heat rays and whilst not dismissed out of hand they're considered to be rather inefficient as humans are quite wet and cooking them to death takes a lot of energy or a lot of time.

Pulse lasers are referred to as blasters, and work by explosively vaporizing a small portion of the target, pausing whilst the vapor expands and blows out of the way, then pulsing again on the same spot to deepen the hole, hopefully making a hole deep enough to do disabling or lethal damage.

An example laser pistol has the following description:

The light laser pistol is a compact sidearm for concealed carry. Its beam energy is 1.2 kJ, consisting of 60 pulses of 20 J each spaced 4 microseconds apart. It has a sustained rate of fire of 2 shots per second and a safe overheating margin of 8 shots. It masses 0.45 kg and has a 1.5 cm primary aperture. The effective focal range is around 30 meters. It is commonly powered by a 0.15 kg power pack in the grip, which gives 25 full power shots at up to 5 per second. 1.5 cm lens.

Treat that as a sort of ballpark figure for your finger guns. Your fingers probably have a smaller tip, which limits the lens size, which limits effective range, but it isn't like you're trying to make serious weapons here. The key thing to note is that you probably want to be delivering ~ 1 kJ of energy in <1 ms, if you want a weapon that's a significant threat to a (presumably unamored) human.

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100 watts is not very much power. With 100% efficiency, that delivers 100 joules of energy every second, or enough to raise the temperature of just 25 grams of water by 1 degree Celsius. Human skin burns at somewhat above 40°C- you'll need to point a laser at a specific spot on someone's body for a solid 20 seconds to even begin to burn even a tiny percentage of their body mass.

Searching for 100W lasers yields tools capable of engraving and cutting materials a few millimeters thick. You are not going to laser-engrave someone to death.

EDIT: I see now that the 100W requirement has been removed. With no upper limit on power, you can deliver as much energy as you want in as short a time as you want, making the laser arbitrarily lethal. Get a petawatt laser, and you'll be able to deliver an atomic bomb's worth of energy in a fraction of second - that ought to be sufficient to do some damage. The question as currently stated is a bit like asking if an arbitrary projectile can kill, but not specifying if you're talking about a spitball or tank shell. Just about anything can kill if it delivers enough energy fast enough.

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    $\begingroup$ Human skin does not burn at 40 °C. People who have 40 °C fever do not catch fire. $\endgroup$
    – AlexP
    Commented Apr 26 at 14:45
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    $\begingroup$ @AlexP Burn injury begins to occur at 44°C: pubmed.ncbi.nlm.nih.gov/28536038. I think it's fair to call that "around 40°C", and provides an estimate on the generous side of what the OP is trying to accomplish. $\endgroup$ Commented Apr 26 at 15:01
  • $\begingroup$ @AlexP I burn when showering with girls, I guess it's dependant on personal heat tolerance $\endgroup$
    – Xenophile
    Commented Apr 26 at 15:51
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    $\begingroup$ @Xenophile if she's burning you in the shower, consider the possibility she might actually be some kind of demon. $\endgroup$ Commented Apr 26 at 16:06
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    $\begingroup$ @Coolcats112 You might be able to burn a small amount of material with low heat capacity by aiming a low-power laser at it for a long time. But you're not going to easily burn a person with 1W - that isn't even enough to turn on an LED light bulb. $\endgroup$ Commented Apr 26 at 16:21
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I doubt 100 W would be effective at killing, maybe at permanently disabling a target, but not killing:

  • no serious target would go around naked (your laser is tuned at max skin absorption).
  • even a kW laser takes some time to pierce through a mere chicken breast: before killing a target, you would need them to stay still in place while you don't change the aiming and carve your way through the body until you pierce a vital organ. I have accidentally got a few pulse of laser on my elbow, and I can assure you that you WILL move once you get hit.
  • unless you can see in the IR, you will not see where you are hitting with your laser.

You could manage to blind a human, sure.

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  • $\begingroup$ Would setting people on fire work? Also, i heard pulsed lasers can do cool stuff but i do not what would happen if they had a wattage of 100 watts compared to a petawatt. $\endgroup$ Commented Apr 26 at 14:13
  • $\begingroup$ @Coolcats112: Human bodies need an accelerant to burn. There is just too much water in a human body. $\endgroup$
    – AlexP
    Commented Apr 26 at 14:47
  • $\begingroup$ @AlexP there is hair and fat tissue on human bodies $\endgroup$
    – Xenophile
    Commented Apr 26 at 15:53
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A laser of low power will blind someone. A laser with decent power will blister skin, set clothes on fire, and blind anyone looking at the person you're shooting at. A laser of really high power will cause the water within a human body to flash-vaporize, effectively causing a small explosion that serves to further damage nearby tissues, in addition to the severe burns you'll be giving them. You'll probably also blind everyone in a 1-mile radius.

That said, almost all fiction ever ignores the issue of blinding people, for the simple reason that it's not fun. You don't want your MC to go around blinding every ally and enemy on the battlefield accidentally.

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  • $\begingroup$ Also note that the specific wavelength range given, near infrared, is particularly unsafe for vision because it is focused by the cornea and lens and reaches the retina, but does not cause the protective response that a visible laser would have. Longer wavelengths are considered "eye-safe" because they are absorbed by the cornea. A mid to far infrared laser would probably only blind you if it hits your eyes directly. However, it'd also be a poor choice for a weapon due to atmospheric absorption, diffraction limits, etc. $\endgroup$ Commented Apr 26 at 23:40

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