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So, I've been trying to think of ways to have a sci-fi "laser beam" in a setting that at least gives a fig leaf of realism. After reading through many other posts here it's become clear that as personal-scale weapons, lasers pretty much suck. Heating the surface of something is a poor way to inflict damage.

But who doesn't want to have a sleek, heavy rifle that projects a glowing beam that cuts things in half? So my question is, is there any way we can combine different technologies to get this effect?

My initial thought, inspired by the mass effect series, was a combination of a laser and a coilgun which is designed to fire a laser to blast a channel through the air, followed immediately by a thin (3mm or so) stream of white-hot liquid metal electromagnetically accelerated to hypersonic velocity.

Obviously, this would still require some pretty sci-fi power storage and may still fall foul of the "you might as well just launch the power cell at them" issue. And recoil would probably be pretty gnarly. But wouldn't a half-second pulse from such a weapon allow you to, say, slice a man-sized steel-armored combat robot in half, leaving cool molten edges on the cut?

If not this, are there any other potential explanations for a weapon that bears some resemblance in apparent effect to the iconic sci-fi laser rifle, while giving some concession to the laws of physics?

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    $\begingroup$ What standard you apply? Hard Science? Science Based? Science Fiction? Fantasy? $\endgroup$
    – Trish
    Commented Jun 10 at 9:36
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    $\begingroup$ You can think of an ordinary AR-15 rifle as firing a short, 5.65 mm thick stream of solid metal at the target... And about that half a second pulse, have you tried to compute the weight of the metal fired at the target? In other words, how much does a piece of wire 3 mm thick and 900 meters long weigh? (The answer is about 33 kg or 72 pounds if the wire is made of steel.) $\endgroup$
    – AlexP
    Commented Jun 10 at 9:57
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    $\begingroup$ I'd go with a laser creating a stream of electrically-conductive plasma through which you run an electric current (disruptor). You can stun (like a stun gun), kill (stop a heart), get a nice burn, fry electronics, and it would look like a mini lightning bolt with a sonic boom as the gas accelerates along the beam. $\endgroup$
    – DWKraus
    Commented Jun 10 at 14:13
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    $\begingroup$ Alternatively, a gyrojet is essentially a mini rocket launcher. No recoil, flat trajectory, the projectile accelerates over time (so you could see it when fired), it operates in a vacuum, projectiles could be guided OR explosive ("blaster"), micro-shaped charge (armor-piercing) and you can easily imagine a visible propellant creating a glowing streak. Plus the original designs look cool. en.wikipedia.org/wiki/Gyrojet $\endgroup$
    – DWKraus
    Commented Jun 10 at 14:20
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    $\begingroup$ Save me from the current "realism" craze. One of the many reasons Star Wars Episode IV (1976) is still the second highest grossing movie of all time (adjusted for inflation) is because it didn't worry that much about realism. $\endgroup$
    – JBH
    Commented Jun 10 at 15:47

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Neither low-power laser NOR a railgun round is going to produce a cool looking beam.

You would need to make the laser really, really, really powerful for the glow to be visible in most weather conditions. A laser is invisible in vacuum, and mostly invisible in the air. The only way to make it glow "cinematically" is to make the beam so powerful that it turns the air, vapor, and dust it flies through into plasma. The laser beam would have to be so powerful that the air in its way is heated to around 4000 degrees Celsius. At this point the laser itself is going to be enough to vaporize the target, the target's surroundings, and incinerate everything even adjacent to its path by proximity.

Same with railgun/coilgun rounds, really. As far as we can tell from the scant data we have on actual experimental railguns, their bolts move so fast that even most cameras have a trouble tracking them, never mind the human eye. If you watched me shoot someone with a hypothetical handheld coilgun/railgun rifle, you would not see a cool beam. You would see the target just burst into white-hot mist, and slightly after you would hear the sonic booms of them exploding and a much higher pitched sonic hypersonic crack of the rifle itself.

The only way for the coilgun bolt to leave a visible beam is to make it even more obscenely powerful so that it would convert the air it passes through into plasma that would last a split second AFTER the bolt had passed.

If you combine both a laser and a coilgun and make either/both powerful enough to leave a visible beam, you just made a weapon that can only be sensibly used as anti-battleship gun, best used at the distance of kilometers. If you shot such coilgun at me at the standard distance handheld guns are used, you would likely kill us both, leave a crater of molten rock, and incinerate the entire neighborhood.

There IS however, a 100× simpler, cheaper, far more efficient, and easy solution to this: tracer rounds. We already developed a weapon that can reliably kill the target at sensible distances while leaving a cool visible beam: simply a rifle with a tracer round in it.

Simply have your space-marines or whatever shoot massively hypersonic incendiary phosphorus bullets at one another. A hit from one would reliably kill, incinerate, melt metal, and leave a split second beam of light in its path. It might even work in space if the round carries some oxygen in it.

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    $\begingroup$ A solid oxidiser mixed with the tracer material would work better than a source of actual O₂ for space tracer rounds, and we have those from rockets (and something similar in thermite, where the oxygen source is rust) - but actually tracer rounds already include this $\endgroup$
    – Chris H
    Commented Jun 11 at 8:41
  • $\begingroup$ The coil/rail gun described could be incredibly cool. The current fad is just the lasers, but why not have something feel incredibly powerful. You aim, you pull the trigger, something explodes in a ball of white hot metal and flames. Sure you'll have to explain some way the rail gun doesn't explode the person shooting, as each action has an equal opposite reaction, but why not imagine something new that is cool? The line from Taken is brilliant because it says the same as so many, but in a very different format. He's got a very specific eet of skills... Do the same with guns. $\endgroup$
    – Trioxidane
    Commented Jun 11 at 12:25
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    $\begingroup$ @Trioxidane shooting someone with such a powerful railgun while in the vacuum of space would have one extra feature: vacuum is near perfect insulation. So if you blast someone and they turn into a ball of white-glowing molten slag, they will remain a ball of molten slag for a long time, because the heat has no way to escape except as radiation. $\endgroup$ Commented Jun 12 at 7:34
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Frame Challenge

The problems with Laser Weaponary in general is people trying to keep them realistic and with realistic power storage and delivery mechanism(s).

If you have a world where you can both use a Laser Beam to punch a hole in the air and fire a hypersonic projectile, both within fractions of a second of each other - you have enough power and power delivery to realistically do whatever you want.

Which brings me to my first part of the Frame Challenge:

Splitting the energy between two different modes of damage is generally not advisable

When you want a lethal effect on target, you want to use the barest minimum amount of energy necessary (will cover in a moment) whilst also maximizing the amount that is dumped into the target.

Consider a hunting round of ammunition, it is designed that on impact it spreads apart, slowing down very quickly, dumping all of that kinetic energy into the target, not over-penetrating, and delivering a quick and humane kill.

Apart from the energy lost due to Friction, sound and heat - the majority of the energy is in the Bullet and the majority of that is dumped into the target.

Now - Barest minimum Energy is because you want to be able to carry as much ammunition you can for a given weight/space - Overkill comes at a cost (logistically speaking)

You would have a better weapon in either sending all the Energy to the Laser Beam (which actually can do some rather nasty things on target if there is sufficient energy) or sending it all to the projectile.

Second part:

Laser Weaponary can be cool and effective

Now, Dust and small particles not withstanding, so long as you can get the Wattage high enough and have a means to counteract blooming (Just like Star Trek had a Heisenberg compensator for the transporters, your Laser weapons have a Bloom inhibitor!) Lasers are great choice for a weapon:

  • No recoil
  • No explosive parts
  • No Bullet drop or windage
  • No Muzzle report

And the effect on target of being able to cut people in half is not unrealistic per se, so long as you have sufficient wattage.

To conclude

Lasers are cool, splitting your power between destructive methods is questionable and if you have a portable power source capable of doing what you say - just use Lasers!

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    $\begingroup$ Thank you for pointing out that trying to crowbar fantasy into science is just another form of fantasy. $\endgroup$
    – JBH
    Commented Jun 10 at 15:48
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After reading through many other posts here it's become clear that as personal-scale weapons, lasers pretty much suck. Heating the surface of something is a poor way to inflict damage.

You've been reading the wrong posts.

A suitably intense laser pulse (may joules delivered in microseconds, or shorter, giving peak powers of many megawatts at a minimum) flashes a small portion of the target into plasma. The plasma expands rapidly, causing mechanical damage to the material around the target spot, eke. explosive vaporization. This tears softer material, fractures harder kinds. The puff of plasma dissipates in an instant (it will be moving supersonically in air, I believe) and a second pulse delivered shortly after the first will deepen and widen the hole. Repeat until you've bored a hole through the target, reached depth limits caused by target materials an optics, or the target moves out of the way.

It doesn't kill by burning the target, but by drilling clean through it. Admittedly, this isn't much like a scifi laser, slicing neatly through things, but perhaps a little more like a scifi blaster, but it isn't quite so far away as you might think. Rayleigh scattering in air is strongly wavelength dependent, so green or blue beams are more clearly visible than red for the same beam power. Bright beams are undesirable (because you want that energy to zap the target, not look pretty) but are unavoidable which is perhaps what you were looking for.

A beam modulated to produce multiple short pulse trains, each pulse train spaced from the next by a brief moment, could be played across the target and drill multiple channels through it, potentially enough together that the remaining material (if any) is insufficiently strong to hold it together. You won't get clean wound edges, and they might not glow, but you have unambiguously just sliced something up with a big ol' glowing beam of death. It'll probably make a loud bang or buzz, though. Not "pew". Sorry.

As much as it pains me to admit it though, lasers do have issues with atmospheric breakdown and so their effectiveness becomes sharply limited in rain, or cloud, or very dusty or smoky air, especially if your enemies can make very tough and highly refractory armor out of some kind of nanotube composite.

a thin (3mm or so) stream of white-hot liquid metal electromagnetically accelerated to hypersonic velocity.

Liquids really aren't very useful as projectiles. Even the nicest, smoothest laminar jet will diverge and deform because you can't perfectly accelerate each particle in the same direction at the same speed and even if you could thermal effects (which will be quite strong in molten metal!) will cause jet-disrupting effects. In order to maximize penetration, you need long, narrow and perfectly straight penetrators, and a swept liquid jet isn't really that. It'll slice an unarmored human in half, but you can do that with explosive projectiles from conventional weapons, too.

If you can produce a hypersonic jet, you're probably just as capable of shooting a rapid stream of needle-like projectiles, too. You can save all the energy you would have used melting the metal and against soft or lightly-armored targets you'll slice em up well enough.

A laser-evacuated vacuum channel will probably collapse too quickly to be of use, though, for any kind of solid projectile. Those things make more sense for shooting fast (eg. > or >> .14c) particle beams through, and whilst those can be glowy beams o' death that can melt things in half, the major problem you (and everyone nearby) will face is the horrendous amount of radiation they'll spray out in all directions to the point where there'll be only a short span of time between people going "ooh" at how awesome and badass you look, and "argh" as fatal radiation poisoning sets in.

Back to the drawing board with you, I think.

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  • $\begingroup$ As for using highly refractory armor, I don't think this could work on human scale. Any armor small enough to not be cumbersome will not be thick enough to stop the heat from cooking the wearer inside. $\endgroup$ Commented Jun 12 at 7:51
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    $\begingroup$ @GoingDurden it isn't about being cooked, it is about requiring a light intensity for flash vaporization that's sufficiently high that the laser beam will inevitably trigger a cascade brakedown in the air it is passing through. Such an armor effectively makes blaster-mode lasers ineffective, and non-blaster-mode lasers aren't obviously any better than any other kind of weapon and under many circumstances they're unambiguously worse. $\endgroup$ Commented Jun 12 at 13:42
  • $\begingroup$ Upped the answer for pointing out the "plasma puff" mechanism. Although "puff" is an understatement. There are lasers in laboratories that can trigger nuclear fusion with nano second laser "puffs". The NOVA laser was able to deliver "puffs" of 100 kilojoules and was build in the '80s. That is 20 grams of TNT. $\endgroup$ Commented 2 days ago
  • $\begingroup$ @MennovanLavieren 100 kJ is pretty excessive for an antipersonnel laser, and higher pulse energies for the same pulse length mean you're more likely to trigger atmospheric breakdown, too. You probably don't want pulses of much more than 100 J or so, and you probably don't need more than 100 pulses in a burst to drill a hole through a reasonably tough target. $\endgroup$ Commented 2 days ago
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Antimatter rifle

Yes, this is just replacing a known problem with a bunch of unknown problems, such as antimatter production and storage. But in my opinion the uncertainty of technological progress is what makes sci-fi cool: in the 1970s it wasn't as obvious that laser rifles wouldn't be practical, and currently it is not obvious whether antimatter rifles will be.

If you were able to store antimatter protons and electromagnetically accelerate them into a high-speed stream, it would certainly wreak havoc on anything it hits. The collisions with air molecules would give the glowing plasma beam.

The mass and energy requirements of the weapon would be very modest, with a 5 kJ shot needing just picograms of antimatter and 0.1 Wh of electricity for acceleration.

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  • $\begingroup$ How would you stop an antimatter round from damaging the shooter the moment the antimatter round left the rifle? $\endgroup$
    – Jimmery
    Commented Jun 11 at 0:47
  • $\begingroup$ @Jimmery Magic! That is to say, science! You simply use a magnetically shielded containment system with refracted polarization and dual-thrust ion beams. $\endgroup$ Commented Jun 11 at 3:04
  • $\begingroup$ @Jimmery It would probably be easier to form it as a stream of particles instead of a solid round. Antimatter reacts to electromagnetic fields, so the challenge is similar to guiding the proton beam in medical operations, or to guiding plasma in fusion reactors. Not easy, but there are ways to do it. Regarding collisions with air, the first particles to leave the muzzle would give off a flash of energy, so the shooter would indeed need some level of protective shield. $\endgroup$
    – jpa
    Commented Jun 11 at 6:19
  • $\begingroup$ @jpa "the first particles to leave the muzzle would give off a flash of energy" - I think you are seriously underestimating the explosive power of antimatter. If a gram of hydrogen is reacted with a gram of antihydrogen it would release 2e-3 * (3e8)2 = 18e13 joules ~ 40 kilotonnes of TNT which sounds like a small nuclear bomb. Even a stream of particles would result in a powerful explosion as soon as they hit the air in front of the weapon. $\endgroup$
    – Jimmery
    Commented Jun 11 at 13:08
  • $\begingroup$ @Jimmery The size of explosion can be controlled by controlling the amount of antimatter in the shot. The first few air particle hits would emit enough heat to cause a shock wave to clear the path. Even if all air had to be annihilated, a 1 µm beam would give off 1 MJ in the first 10 meters - quite manageable with a reflective shield. $\endgroup$
    – jpa
    Commented Jun 11 at 14:48
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There's a really cool technology that the US Army looked into decades ago called "ETC". ETC was essentially a regular tank round and casing except instead of a primer it uses a "plasma cartridge", this was just a container which high voltage electricity would flow through to create a plasma which ignited the regular propellant charge more efficiently than regular primers. This lead to increased consistency and muzzle velocity due to the propellant burning more completely.

Now, the US Army used bog standard electrical connecters and wires to create that plasma, however if you really wanted to, its also possible to create plasma using a laser focused through a gas of some sort.

Its not completely infeasible to imagine a more compact version of this tech even today, so I guess you could in theory make a "Laserthermal-chemical rifle" or "LTC rifle".

I know it doesn't exactly cut people in half but it is technically a laser weapon. Actually if you made it into a 20mm shoulder fired weapon, it could certainly tear someone in half. Bonus points if you somehow manage to make a 20mm thermobaric round to burn everything as well.

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Closest analog

The problem is that you have a fantasy that you want to make reality. The easiest is just accepting you want something sci-fi and run with it, making your own explanations as you go. Here's the best thing though. You don't need to. The laser rifles in Star Wars, Star Treck, Moonraker and whatever else work regardless.

If you do want the 'cool cinematic laser' explained by science as close as possible, you can just grab any closest analog and find reasons why it would work that way.

For this example I'll assume the 'slow' lasers like in Star Wars, instead of the instant ones of Star Treck, which are basically just lasers made visible (and some magical pulsed property for damage). The slow variety is originally depicted as an oblong piece of light flying over the screen, as we'll ignore the new movie where they added more lightning and particle effects. What looks closest?

Any oblong metal, or possibly a ball or bullet moving fast enough to appear oblong, can do the trick. If you've seem (industrial) smithies you'll know that metal heated enough will give off a bright light. This is also used in old fashioned light bulbs and TL lamps for example. We can use this to fire a superheated metal, chemical or whatnot. It'll fly slower, but we can explain that in this day and age this is required to be effective against armour. Regular weapons do not do the trick any more. So we need a superheated rod or ball fly at the enemy. If there's shields it becomes even easier to explain. They might work as the shields in Dune, where you need to move slowly to penetrate the shield. Maybe superheating a bullet makes the shield incapable to effectively see and counteract the vibrations of the superheated molecules, allowing them tobe effective.

It is more about the explanation why you use it than the scientific explanation how it works, or even better, no explanation at all.

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