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I'm working on a game with combat between spaceships. It will not be hard sci-fi, but I'd like to base the mechanics on (simplifications of) real physics.

When it comes to laser-weapons, I would like to include lasers of different wavelengths, preferably in the microwave (maser), visual (laser) and x-ray/gamma-ray range (graser). I wish to know what the realistic effects the wavelength would have on a laser's effectiveness as a weapon are.

I know (but correct me if I'm wrong) that the beam of a shorter wavelength laser retains its focus for longer and would thus have a larger effective range. Also, there currently aren't any "mirrors" that reflect x-rays/gamma-rays which means such lasers can't use a resonance cavity, which means you need a longer "barrel" and/or get less energy output. And obviously the shorter wavelength beams carry more energy per photon, but I don't know if that has any significant effects.

To split off my general question in three more concrete examples:

  • Assuming a laser designed to output a fixed wavelength, what are the advantages and disadvantages of such a laser with a shorter or longer wavelength? Are there any performance characteristics (for example, range, damage on target, size/mass of the laser, cooling/recharge time) that would be significantly changed between, say, a 100 MW maser, laser or graser? (Or is there a limiting factor that prevents you from pumping a large amount of energy in one particular wavelenght of laser?)

  • Assume a Free Elector Laser, which can output different wavelength laser beams. With the design of the laser fixed for all different wavelengths (though minor mechanical tweaks when changing between wavelengths, like sliding mirrors in and out of the beam, is allowed), does this have different effects on the effectiveness of the laser than in the fixed design per wavelength above?

  • Are there any effects exclusive to the very high or low end of the wavelength spectrum, such that the visual wavelength laser's isn't simply the midpoint between the microwave and x-ray/gamma-ray laser in terms of performance?

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  • $\begingroup$ A lot of this question is basically a google search. There's an enormous amount of information on the relationship between wavelength and power when it comes to lasers. Specifically " The power of a laser beam depends on the energy levels of the electrons in the atoms of the material used to produce it, generally called the “lasing” material. The energy level of the photons produced by the lasing material is inversely proportional to the wavelength of the light produced by the lasing material." escooptics.com/blogs/news/… $\endgroup$ – Morris The Cat Jul 15 at 13:38
  • $\begingroup$ Yes, the energy per photon increases as the wavelength gets shorter. But that does not mean by itself that a shorter wavelength laser is automatically more powerful. The laser YAL used to shoot down a missile from hundreds of miles away was infrared. A laserpointer has a shorter wavelength, but is obviously less powerful. What I'm hoping to learn is what the difference is between, say, a 100 MW x-ray laser vs a 100MW visual light laser fired at a ship. My google-fu wasn't good enough to find detailed information on that, as most sources on laser-nitty-gritty aren't about sci-fi battles. $\endgroup$ – bificommander Jul 15 at 13:52
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    $\begingroup$ Having now cobbled together an answer, it is clear that you are asking far too many different questions at once. You need to focus on one issue (or a much more tightly related set of issues) if you're going to get good answers; if I tried to go into detail on all the things you're interested in I'd be here all day. $\endgroup$ – Starfish Prime Jul 15 at 14:09
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    $\begingroup$ I have to agree this question is a little too broad. $\endgroup$ – Trevor Jul 15 at 14:17
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    $\begingroup$ Obligatory mentions of Atomic Rocket and the ToughSF blog, which you may find useful $\endgroup$ – Eth Jul 15 at 15:16
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The question was slightly editted and clarified in the original post and some comments, so my original answer has been replaced and you can find it in the edit history if you were interested. I've ignore some parts of the original question, because it was too broad.

what are the advantages and disadvantages of... [a] 100 MW maser, laser or graser?

Masers may be generated simply and efficiently. We can do that well enough nowadays... something like a gyrotron is decades old design, and I believe we can get efficiencies of at least 50%, which is pretty good. The range of a maser is more limited than devices that emit shorter wavelengths due to diffraction issues.

(note that in really old scifi, masers may have been used simply because there were no lasers yet, and there was a time when lasers might have been called "optical masers")

Lasers (by which I'm choosing to mean "things that emit visible and near-visible light") are harder to generate (read: needs more clever engineering, generates more heat, etc etc) but have the advantage that they have a much longer potential range as they suffer less from diffraction due to their shorter wavelengths. We also have a good knowledge of optics, and there are plenty of ways to bend and focus visible light. Efficiencies are likely to be lower than masers, but needn't be terrible, especially in a fancy future scifi setting.

Grasers aren't quite scifi... bomb-pumped nuclear lasers have been around in theory for decades. The biggest problem with them is that as the beams can't reasonably be reflected, and any attempt to focus them is probably going to require something like a zone plate which means you either have to put up with unfocussed beams (read: short range) or losing at least 50% of your emitted power to the opaque bits on your zone plate. Efficiencies are likely to be very poor... maybe only a few percent. As a weapon, they might be found on nuclear missiles which can get close enough to the target to zap it, rather than trying to build one onto a warship.

what the difference is between, say, a 100 MW x-ray laser vs a 100MW visual light laser fired at a ship

There are a number of important differences. An obvious one is potential range... the radius of the focussed spot at the target (which you want to be as small as possible) is proportional to the wavelength of the light the laser emits. X-ray light has less than a twentieth of the wavelength of visible light, which gives a massive potential range advatange.

Both lasers, when they're in their killing range will generate plasma when they hit their target. For the visible light laser, this is inconvenient because the plasma will be opaque to the radiation it is emitting, and so the laser will have to stop, wait for the plasma to dissipate, and then start again so as not to waste power on heating the plasma instead of zapping the target.

The x-ray laser is under no such limitation, and can keep firing for as long as you like, and pulse as fast as is practical. The drilling speed of an x-ray laser at shorter ranges is likely to exceed the speed of sound in the target's armour. Each pulse of the laser will generate a shockwave in the armour, and these shockwaves will all merge together at the back face of the armour producing quite a bang.

At any range, an x-ray laser of suitably short wavelength will ionise material it is incident upon. This will damage the chemical and crystalline structure of the target (important for handwavium "thermal superconductors") and interfere with electrical and electronic systems.

X-rays are obviously highly penetrating. They have a measurable attenuation length in matter, meaning that the energy deposited in the target drops off exponentially with depth. This means that it may be possible for a beam to shine straight through thin or low density materials and cook whatever is underneath (eg. the meatbags flying the ship), even if it isn't actually powerful enough to melt the armour.


Finally, and this is perhaps the most important thing... X-ray lasers are going to be big, and they're going to be inefficient. You pretty much have to use a free electron laser, and those things get pretty hefty if you want small wavelengths. You have two choices... a linear particle accelerator (aka a LINAC) or a synchrotron. The former can be very, very long... the European XFEL is over 2km long, for example, though you could probably get away with a more modest accelerator a mere few hundred metres long. You can wrap this around into a doughnut-shaped synchrotron to be more compact, but whenever you bend the electron beam you will lose energy to synchrotron radiation, and that means lower efficiency, more heat output and larger power requirements.

You might think that you could use a super-compact wakefield accelerator (with accelerations to GeV energy levels over metres instead of over hundreds of metres), but alas current designs are not actually very efficient (certainly no more than 30%, excluding seed beam, FEL and optics losses) so again: more heat, higher power requirements, lower output. TANSTAAFL. Its enough to make you just throw up your hands in despair and just use a normal laser instead.

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  • $\begingroup$ Sorry if it is too broad. Although as a side note, I didn't mean I needed information on every category I mentioned, but more if any one category was something a wavelength change would always strongly affect. I don't know if that narrows it down, but I'll edit the question. I know that for the low-end, masers are popular in sci-fi at least, so I assumed that they would at least have a theoretical usefulness. $\endgroup$ – bificommander Jul 15 at 14:21
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I was going to ask this question but you beat me to it.

I have the sneaking suspicion that microwave lasers are secretly very good, efficient, and critically underrated, as they are good for frying electronics and making the recipient's craft inoperable while having a low energy per photon. If energy shields are a thing, it's a common sci-fi video game convention that EMPs wreak havoc on them.

X-rays and gamma rays may very well be an energy inefficiency trap if mirror plating isn't allowed (in which case you might prefer a more efficient visible-spectrum or infrared laser). If mirror plating is a problem, then definitely use an X-ray laser.

A common misconception is that "higher frequency = more energy = more damage". In practice, what's more important is that the energy interacts with (is absorbed by) its intended target. In theory, if you used extremely high-frequency EM radiation, the energy cost will be prohibitive and a good amount of the blast might simply punch through whatever you're aiming at. Sure you might do a lot of damage, but it's a horrid waste of energy when you could have used a simple microwave laser and nixed the enemy's electronics.

An extreme example of "energy input != damage": Neutrinos. Particles that hardly interact with matter. You could have a particle beam that fires massive bursts of neutrinos, and chances are they will simply pass through the recipient.

My overall answer to this question: X-ray laser paired with a microwave laser. This thwarts mirroring defenses while giving you the option of punching holes in hostile craft or simply disabling them.

Interestingly enough, I've been playing a lot of Freespace 2 lately, and I often pair the Akheton SDG (EMP bolt/system disruption) with Subach X-ray lasers.

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