Hypothetical laser gun

[DarkElfDude]

okay let's be honest, every sci-fan has wanted to make a laser gun before, but how to actually do it is the problem. I've come up with a few ideas but feel free to discuss or add your own

-multi terawatt beam, probably the simplest way, after all, people have already made lasers capable of burning through cloth, and the u.s navy is already working on a missile defense system using lasers. all it would take to make a deadly laser would be a sufficient amount of power and adequate cooling systems

-plasma, now here is where it gets more complicated, a plasma rifle would take a way to keep the plasma in a more dense form since plasma is more of a superheated gas it would most likely just dissipate and melt the barrel (and maybe the user)

-gold particles, i honestly have no idea how somone could get this to work in a way that could be fitted to use in a rifle but if it somehow was made it would be more of just a heatblast, although scientists say that when the hadron collider slams two gold particles together it creates the a tempature higher than any stars ever discovered

[Lvl 2 Expert]

The collisions at the large hadron colliderbeing energetic has less to so with them using gold particles and more with them having a huge particle accelerator.

There are quite small quite effective linear accelerators now, but honestly if you're using magnetism to propel your projectiles anyway I'd use heavier projectiles than single atoms and just build a proper railgun. That way you can kill people quickly rather than maybe give them cancer somewhere in the next few decades.

[Manga Shoggoth]

When I was at university doing my final year project¹, the person next to me was building a laser.

It was essentially a vaccum chamber created from several rectangular strips of perspex, with two strips of copper running down opposite sides. A vacuum pump brought it down to low pressures and a combination of a high voltage supply and a spark plug supplied the energy. A mirror at one end stopped it firing in both directions...

When the pressure got low enough you got sparks jumping between the copper strips, and as it approached ideal lasing conditions the sparks started to wisen. When it was lasing you effectively had a single spark jumping across the length of the two strips. It was probably the coolest² of the experiments we had that year.

Nitrogen lases in the ultra-violet, so to see the actual effects you had to place a container of flourescin at the business end - although one of the Doctors accidentally stuck their hand in the wrong place and ended up with a very well defined case of artificial sunburn.




¹ I got the Hall Effect in a low pressure helium plasma. It wasn't nearly as exciting as it sounds.
² Including the one that used liquid nitrogen.

[Telok]

One issue with lasers is which wavelength to use. Moat people think about IR, UV, and visible light lasers, but you can theoretically lase across the entire EM spectrum.

Microwave lasers should be interesting, and I'd be interested to know what a radio laser would do to electronics. One of the important aspects this is thay as you use shorter and shorter wavelengths the light wave itself becomes more damaging. So you need to produce less light, although the overall energy input will probably remain similar.

[Tvtyrant]

The US military had had working laser guns for decades, and they have gone from Boeing held single shots to normal artilley sized in the last decade or so. The issue is getting portable power more then anything, energy storage has not had the kinds of advances we expected.

[factotum]

I love the way you say that the only problems getting a multi terawatt laser to work are "sufficient amount of power" and "adequate cooling systems", when those are the really difficult things! A portable power supply capable of providing that sort of power is totally beyond any tech we're even looking at right now--bear in mind that a typical electric car has only about 30-40 kWh of power in its batteries, and those weigh half a ton. As for cooling, if the laser itself dissipates 1TW and is 99% efficient, that's still 10GW of waste heat you have to somehow get rid of to avoid cooking the user.

[Manga Shoggoth]

One issue with lasers is which wavelength to use. Moat people think about IR, UV, and visible light lasers, but you can theoretically lase across the entire EM spectrum.

Microwave lasers should be interesting, and I'd be interested to know what a radio laser would do to electronics. One of the important aspects this is thay as you use shorter and shorter wavelengths the light wave itself becomes more damaging. So you need to produce less light, although the overall energy input will probably remain similar.

Fun fact: Masers were the predecessors to lasers - the first maser was built in 1953, and the first laser in 1960.

[DarkElfDude]

I love the way you say that the only problems getting a multi terawatt laser to work are "sufficient amount of power" and "adequate cooling systems", when those are the really difficult things! A portable power supply capable of providing that sort of power is totally beyond any tech we're even looking at right now--bear in mind that a typical electric car has only about 30-40 kWh of power in its batteries, and those weigh half a ton. As for cooling, if the laser itself dissipates 1TW and is 99% efficient, that's still 10GW of waste heat you have to somehow get rid of to avoid cooking the user.

When i said only I meant that those were ONLY the two major problems, I didn't mean they would by any means be easy to solve

the overheating problem might be able to be solved by releasing the heat toward the front of the gun so it would heat the target but unless you have some sort of heat sheild that would probably still destroy the user and or device

[Lord Torath]

You also have the problem of heat blooms in the air your laser is traveling through. A stiff breeze can blow your laser off course. Well, really pull your laser off course, since it will tend to bend against the wind, rather than with the wind. At least if I recall my atmospheric physics correctly...

[MisterMan]

What theoretical advantages do directed energy weapons have over kinetic weapons?

I know they have the “cool factor” like big gasoline explosions in movies. But what else is there?

Portable single user transportation devices like jet packs have strong theoretical market demands, so to speak. (Edit: brought up as an example of another long-sought technology that has stalled through the 20th century and into the 21st). I don’t see much use for directed energy weapons. They’re just so incredibly energy inefficient compared to kinetic weapons, when it comes to damage on target.

[Tvtyrant]

What theoretical advantages do directed energy weapons have over kinetic weapons?

I know they have the “cool factor” like big gasoline explosions in movies. But what else is there?

Portable single user transportation devices like jet packs have strong theoretical market demands, so to speak. (Edit: brought up as an example of another long-sought technology that has stalled through the 20th century and into the 21st). I don’t see much use for directed energy weapons. They’re just so incredibly energy inefficient compared to kinetic weapons, when it comes to damage on target.

Small damage area and nearly perfect accuracy are the biggest ones. A laser burns a little hole in something, so you can destroy a drone's computer or a ship's motor and leave the body intact for capture. They also can hit very fast moving targets because the time between firing and hitting is so short, so they are better at hitting rockets/missiles. They are also cheap to fire, so you don't spend a million dollar missile each time you want to shoot a $400 mass produced drone out of the sky.

[Xyril]

-plasma, now here is where it gets more complicated, a plasma rifle would take a way to keep the plasma in a more dense form since plasma is more of a superheated gas it would most likely just dissipate and melt the barrel (and maybe the user)

Strictly speaking, plasma just needs to be ionized gas--something that can be done at more lower temperatures by applying electrical power. Any decent university (or for that matter, a lot of bars and diners) will routinely work with plasma. With enough applied electric field, you can etch through materials without getting too hot (and by "too hot" I mean melting the metal or glass used to contain the plasma.)

The big limitation I see is the distance. Even within a low pressure chamber the size of a microwave, mean free path becomes a big issue has your ions lose energy to collisions with gas molecules. If you jack up the power (which you would probably have to in order to cause damage fast enough to be tactically useful) you would have a lot more momentum to start with, meaning you could afford to lose more before becoming useless. Still, you would lose a huge fraction of your power over just a hundred feet or so. Worse, this energy doesn't just disappear--most of it will go into random collisions with air molecules closest to your gun. Right now, this would just mean that the plasma dissipates and starts heating up the air closest to your friendlies. However, if you're coming up with a way to make sure that your plasma can traverse a useful distance, I have no clue how this would work. It could potentially end up like firing a giant shotgun full of superballs through a thick forest--most of the balls will keep going in the general direction of "away from shooter," but a few will hit something and bounce off in a different direction. Even if the proportion of plasma ions that bounce back is small, remember that the shooter will be exposed to loose plasma for every shot fired.

[MisterMan]

Small damage area and nearly perfect accuracy are the biggest ones. A laser burns a little hole in something, so you can destroy a drone's computer or a ship's motor and leave the body intact for capture. They also can hit very fast moving targets because the time between firing and hitting is so short, so they are better at hitting rockets/missiles. They are also cheap to fire, so you don't spend a million dollar missile each time you want to shoot a $400 mass produced drone out of the sky.

Interceptor missiles are not kinetic projectiles; kinetic projectiles are bullets more or less. Rail guns, explosive driven rifles, etc. They are the cheapest option for any firing solution requiring damage on target.

However, you brought up the opposite: not wanting damage on target! That’s extremely niche, but it is a unique laser capability. In theory a laser might be able to fire faster than a rail gun for interceptor work, but in practice that’s not been the case at all. Various kinetic projectile solutions have proven cheaper, more reliable, more versatile, and easier to operate and maintain.

Accuracy isn’t necessarily true, given that computerized firing solutions are about as accurate with wind deflection etc for kinetics as for lasers. Time to target is legitimate but I’m not sure at what point that becomes relevant.

Finally the most common sci-fi application for energy weapons, space, is the best place imaginable for kinetics.

[Brother Oni]

However, you brought up the opposite: not wanting damage on target! That’s extremely niche, but it is a unique laser capability. In theory a laser might be able to fire faster than a rail gun for interceptor work, but in practice that’s not been the case at all. Various kinetic projectile solutions have proven cheaper, more reliable, more versatile, and easier to operate and maintain.

Depends on the system. The current US Navy railgun prototypes have 'barrel' life measured in the few tens of shots.

Accuracy isn’t necessarily true, given that computerized firing solutions are about as accurate with wind deflection etc for kinetics as for lasers. Time to target is legitimate but I’m not sure at what point that becomes relevant.

Barrel vibration is most definitely a thing, in addition to variations in propellant performance for chemical based weapons.

For example, the old 20mm M61A1 Gatling gun used in naval CIWS point defences has a listed dispersion of 8 milliradians diameter, 80 percent circle. At a theoretical engagement distance of 9km (5 nm), that's 80% of the shots it fires, landing in a circle of 72m diameter.

A BrahMos-II antiship missile travelling at Mach 8 will cover that distance in approximately 3.3 seconds, which doesn't leave a lot of time for countermeasures.

Meanwhile a laser can engage at greater distances, more effectively.

Finally the most common sci-fi application for energy weapons, space, is the best place imaginable for kinetics.

Sure, if you're shooting at relatively static targets or are engaging at effectively 'knife fight' distances of less than a couple hundred km and don't care what happens to anything behind the target if you miss.

Space is fine for kinetics until your engagement distances start being measured in the tens of light seconds, at which point pretty much anything that's not travelling at significant proportions of c (or c itself in the case of lasers) are useless as you'll see them coming in plenty of time and can take evasive action.

[Chen]

Space is fine for kinetics until your engagement distances start being measured in the tens of light seconds, at which point pretty much anything that's not travelling at significant proportions of c (or c itself in the case of lasers) are useless as you'll see them coming in plenty of time and can take evasive action.

Mass kinetics would work I think. Like firing the equivalent of buckshot in the area your target is moving through. Very hard to detect that in space, especially if it were electromagnetically propelled and consequently wasn't very hot. Guided missiles that release a field like this could be interesting too.

[Radar]

Accuracy isn’t necessarily true, given that computerized firing solutions are about as accurate with wind deflection etc for kinetics as for lasers. Time to target is legitimate but I’m not sure at what point that becomes relevant.

Aside from mentioned mechanical limitations of kinetic weapons, there is also the obvious fact, that during the time needed for the projectile to hit the estimated position of the target the trajectory of the enemy can change. With laser this simply will not happen. Quick fireing combined with effectively no travel time means you have time to walk your shots if needed with an energy weapon whereas it would not be the case with kinetics. There is a reason last resort anti-missile defences so far were of the spray-and-pray kind (and they did emphasise on spraying hard).

Atmospheric conditions can also be included in targeting computations for the laser by the way.

[Phhase]

One similar idea I've been getting stuck in my head as really cool is the electrolaser. Using a laser, you create a line of ionized air for just a moment, and then slam a lightning bolt through that path. It sounds really cool, but I'm not certain how much the energy cost/destructive force ratio compares to just using the energy to make a stronger laser rather than generating a lightning bolt. It's certainly lower range.

On the topic of plasma, there must be SOME way to create ball lightning. It still seems to be a bunch of contesting theories, but I hear the Spinning Vapor Toroid line of thought has has some comparable results.

[Brother Oni]

Mass kinetics would work I think. Like firing the equivalent of buckshot in the area your target is moving through. Very hard to detect that in space, especially if it were electromagnetically propelled and consequently wasn't very hot. Guided missiles that release a field like this could be interesting too.

Wouldn't the 'buckshot' also need to have a low radar/ladar/sensors profile, or do these sort of detection systems work differently in space?

[Radar]

Wouldn't the 'buckshot' also need to have a low radar/ladar/sensors profile, or do these sort of detection systems work differently in space?

That as well, but the biggest issue is actually different. Buckshot makes sense only if you can get the cloud of bullets thick enough so that the target cannot squeeze between them. Considering how small spaceships would be in comparison to the battle ranges, it makes buckshots either useless or exceedingly expensive and impractical bordering on impossible. At those ranges lasers also become ineffective, since you just cannot keep the beam focused over large distances. The only way to go are either seeker missiles or near c bullets.

[factotum]

At those ranges lasers also become ineffective, since you just cannot keep the beam focused over large distances.

We can focus a laser sufficiently well even now to hit a small mirror left on the Moon by the Apollo astronauts in order to measure its distance?

[Radar]

We can focus a laser sufficiently well even now to hit a small mirror left on the Moon by the Apollo astronauts in order to measure its distance?

Define sufficiently well. It is bright enough that we still can register the light coming back (with telescopes combined with photomultipliers at really low temperatures and even then noise needed to be treated carefully), but I can assure you that the spot being lit on the Moon is way larger then the mirror itself. There is an inherent limit on how well you can keep a light beam focused due to diffraction.

[Chen]

That as well, but the biggest issue is actually different. Buckshot makes sense only if you can get the cloud of bullets thick enough so that the target cannot squeeze between them. Considering how small spaceships would be in comparison to the battle ranges, it makes buckshots either useless or exceedingly expensive and impractical bordering on impossible. At those ranges lasers also become ineffective, since you just cannot keep the beam focused over large distances. The only way to go are either seeker missiles or near c bullets.

Dispersion is a problem. But if space combat actually occurs at very high velocity than buckshot in the missiles probably works better than missiles that need to make contact. If you're moving really fast its hard to change course so avoiding a dense enough cloud of buckshot will be an issue.

Launching the buckshot FROM you ship probably isn't as useful in retrospect, though I guess it could work if you could make a sufficiently thick cloud by somehow limiting dispersal. Sort of like a large net or something. Actually a big enough net made out of carbon nano-tubes or equivalent might work. I seem to recall theories about using something like that against incoming asteroids.

[Tvtyrant]

I'm reasonably certain that space wars are only going to happen in Earth's orbit, maybe as far as the Moon. The Earth is moving away from space colonization, with lower budgets and less interest. Are lasers more useful in ranges from satelites to the Moon is the question.

[Radar]

I'm reasonably certain that space wars are only going to happen in Earth's orbit, maybe as far as the Moon. The Earth is moving away from space colonization, with lower budgets and less interest. Are lasers more useful in ranges from satelites to the Moon is the question.

From simple diffraction limits you can estimate that to get a minimal spot on the target, you would need an aperture of

sqrt(2*distance*wavelength)

and the spot on the target will be twice this size. So given a 200 nm UV laser and 360 000 km distance to the Moon, we get something around a 12 m aperture and a target spot 24 meters wide.

To be honest it is much smaller then I expected and could be better with an X-ray beam due to a smaller wavelength. So currently nowhere near reasonable, but in principle? I think I actually approve.

[Tvtyrant]

From simple diffraction limits you can estimate that to get a minimal spot on the target, you would need an aperture of

sqrt(2*distance*wavelength)

and the spot on the target will be twice this size. So given a 200 nm UV laser and 360 000 km distance to the Moon, we get something around a 12 m aperture and a target spot 24 meters wide.

To be honest it is much smaller then I expected and could be better with an X-ray beam due to a smaller wavelength. So currently nowhere near reasonable, but in principle? I think I actually approve.

I want to believe! Although if we don't make a moon railgun Heinlen's ghost will be sad.

[Brother Oni]

Dispersion is a problem. But if space combat actually occurs at very high velocity than buckshot in the missiles probably works better than missiles that need to make contact. If you're moving really fast its hard to change course so avoiding a dense enough cloud of buckshot will be an issue.

Hmm, I wonder if using bomblets and/or MIRV technology would work - a single missile to get the warhead into the right area, then the warhead separates into an optimal spread pattern of proximity triggered bomblets.

Alternately, take a leaf out of the Macross series and have mini seeker missiles carried by a single larger missile.

[Strigon]

Dispersion is a problem. But if space combat actually occurs at very high velocity than buckshot in the missiles probably works better than missiles that need to make contact. If you're moving really fast its hard to change course so avoiding a dense enough cloud of buckshot will be an issue.

You're thinking in terrestrial terms, here.
In space, how fast you're going has no bearing on how easy it is to avoid an object. It's only a question of time to impact, how far you need to move, and your acceleration. The only time it ever matters how fast you're moving is if you're heading toward or away from the projectile, and even in that case a projectile used in space would likely have to be orders of magnitude faster than the ships in order to actually hit them.

[Chen]

You're thinking in terrestrial terms, here.
In space, how fast you're going has no bearing on how easy it is to avoid an object. It's only a question of time to impact, how far you need to move, and your acceleration. The only time it ever matters how fast you're moving is if you're heading toward or away from the projectile, and even in that case a projectile used in space would likely have to be orders of magnitude faster than the ships in order to actually hit them.

The speed does matter. Detecting a cold bunch of very small objects is non-trivial. Rapid course changes over “short” distances is energy and fuel intensive. The relative speed of the ship and the projectiles matter due to how difficult it would be to detect them and then maneuver around them in time.

[factotum]

The speed does matter. Detecting a cold bunch of very small objects is non-trivial. Rapid course changes over “short” distances is energy and fuel intensive. The relative speed of the ship and the projectiles matter due to how difficult it would be to detect them and then maneuver around them in time.

Energy and fuel intensive really isn't relevant when you're trying to avoid getting destroyed. As for the second half, he already acknowledged that speed might make a difference if you're heading directly toward or away from the incoming fire, but how likely is that? You likely know where the enemy ship is and you know it's likely to be firing at you, so constant random walk and trying to keep as much of your speed vector at right angles to the enemy seem to be things you'd want to be doing.

[Strigon]

The speed does matter. Detecting a cold bunch of very small objects is non-trivial. Rapid course changes over “short” distances is energy and fuel intensive. The relative speed of the ship and the projectiles matter due to how difficult it would be to detect them and then maneuver around them in time.

The thing is, you don't need a "course change" in the conventional sense. If there's a cloud of projectiles say, 500 metres in diameter on an intercept course, then you need to change your position by 500 metres before it arrives. Assuming a constant time to intercept, it takes the exact same amount of force to accomplish that goal whether you're moving at 0.1 m/s or 0.1c. It doesn't matter if that changes your heading by 45 degrees or 0.0082 degrees.