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In every science fiction story, the author seems to use a different color of laser for his ships, usually to distinguish sides in a fight. X-Wings are red. Tie fighters green. The Enterprise has orange phasers, the Borg green.

Leaving aside the fact that you shouldn't be able to see lasers in space, I want to know if there is any technological reason to prefer one laser color to another in space combat, or even to use a laser color not in the visible spectrum, (for that ultra sneaky affect).

We know from physics that different wavelengths of light hold different amounts of energy. The smaller the wavelength and the further along you are in the blue spectrum, the more energy an individual photon has.

If you shot a laser with the same total energy in red or violet light, would one burn through the hull of an enemy ship first or have any other advantage?

Other factors that could make one laser wavelength superior to another are: Would changing the laser's light wavelength make it quicker to fire or be able to fire more frequently because of the energy requirements?

Would the metal of the enemy hull change what wavelenght of light could melt it quicker?

In the end, I want to know what is the optimum laser color for destroying an enemy spacecraft or what factors I can use to figure this out for my own world.

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closed as too broad by MichaelK, Ash, Secespitus, L.Dutch, Frostfyre Sep 26 '17 at 12:23

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ I wrote up an answer, reread it and discovered it said "I don't know"... ;) $\endgroup$ – bowlturner Oct 2 '14 at 17:00
  • $\begingroup$ For use in space only, or in atmosphere too? $\endgroup$ – user243 Oct 2 '14 at 17:09
  • $\begingroup$ @JonofAllTrades My main concern is space, but if space vs atmosphere makes a difference feel free to answer for both. That could create a distinction between space fighters and atmospheric defense and allow one side to lure the other into the atmosphere. $\endgroup$ – Vulcronos Oct 2 '14 at 17:10
  • $\begingroup$ @bowlturner - I did the same thing. $\endgroup$ – Bobson Oct 2 '14 at 19:52
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    $\begingroup$ @Vulcronos I am voting to close this because you have no less than five different questions in this post. And the last one... "I want to know what is the optimum"... is entirely context sensitive and opinion-based. When it comes to weapons there almost never is an "that is best" because — as always — any weapon will produce a reaction. That reaction will produce a counter-reaction. The counter-reaction will produce a counter-counter-reaction and so on. So there is no way to tell "what is best" because there is no "best" and never will be. $\endgroup$ – MichaelK Sep 26 '17 at 9:57
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A higher-frequency laser will generally be more difficult to engineer, as excited electrons revert to a rest state more quickly (proportionally to the cube of the frequency). This is part of why masers came before (visible-wavelength) lasers.

However, for a given focal width, high-frequency photons will remain focused over a greater distance (proportionally to the frequency). If ships are engaging at distances of thousands of kilometers, rather than the ludicrous spitting distance dogfights shown in most science fiction media, this will matter.

The color of the target makes little difference to a laser. Even shiny mirrored surfaces will shatter almost instantly when exposed to megajoules of energy. There's a Reddit discussion (of course) about this which largely aligns with what I've read elsewhere.

Keep in mind that sensors will, per se, be far more vulnerable than ships' hulls. Consider the Iran-Iraq war, where lasers were widely used to blind soldiers, which can be done with a tiny fraction of the energy required to burn skin, let some cut steel. If your opponent can't see, he can't fight; you can cut open his hull later at your leisure.

All this said, because there's been so little real-world experience with laser weapons it's difficult to even make educated guesses.

If you'd like additional reading...

A science-fiction writer gives a brief but useful rant about the misuse of lasers here. I think he's overestimating the impact of reflection at high power levels, but I could be wrong.

The site Rocketpunk Manifesto has some solid examples of laser weapons, and links to Project Rho, which is a gold mine for hard science spacecraft design. If that's your goal, I suggest you read every page of the Project Rho site.

The roleplaying game Traveller is (relatively) hard-science, and the game book Fire, Fusion, and Steel gives useful information on many aspects of spacecraft and weapons. Particularly, it discusses the real physics behind lasers, and why they chose to bend the rules. For what it's worth, in that system the frequency of a laser does not affect its effectiveness; 100 MJ of light focused onto 1 cm2 is equally destructive whether infrared or ultraviolet.

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This is a bit like asking what length of sword is optimal for a weapon. And the answer is the same: "It depends". Weapons have the same engineering properties as many other tools - you have to choose where to make compromises, and you optimise function for the task at hand where possible. Optimising for specific function over generic can be an important factor.

The factors where "it depends" include:

  • Nature of substance that is being damaged. The substance needs to absorb the wavelength that is emitted, and in a way that it heats up and is damaged quickly. You can tune colour here for additional effect, but it is equally valid to just add more power, or to improve targeting so you can aim for the more vulnerable parts of a system.

  • Convenience of generating source. Higher-powered lasers, or those with unusual wavelength properties might be really effective at destroying some things, but in practice may need to be generated using easily damaged, or massive machines.

For your questions in more detail:

If you shot a laser with the same total energy in red or violet light, would one burn through the hull of an enemy ship first or have any other advantage?

Probably not, the whole of the visual spectrum is much the same to a typical metal surface. However, if you extend that to higher and lower wavelengths you might get different absorption characteristics, making some weapons more effective (could use shorter pulses, or overall less energy to breach the same hull). We are talking about percentage differences though, not big factors.

Would changing the laser's light wavelength make it quicker to fire or be able to fire more frequently because of the energy requirements?

That depends on the machinery that makes the laser, and it is not directly dependent on wavelength. However, different laser designs may produce some wavelengths more efficiently than others, so certain colours might be preferred for performance reasons.

Would the metal of the enemy hull change what wavelenght of light could melt it quicker?

It can be a factor, but not always a critical one. See the parameter details in this brochure on industrial cutting lasers. section 5.8, where it is one of 8 or so considerations.

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Because laser weapons will be diffraction limited, the effective range of the weapon is a function of the size of the focusing lens, and inversely proportional to the wavelength.

Therefore, a laser weapon should use the shortest possible wavelength that can be managed with the available technology.

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    $\begingroup$ So in other words, you're suggesting a gamma-ray laser, if possible? $\endgroup$ – Bobson Oct 2 '14 at 17:46
  • $\begingroup$ A gamma-ray laser would have a second advantage: Since it's ionizing radiation (that is, able to rip electrons away from their atoms, and thus to destroy chemical bonds), it would do far more damage than a non-ionizing laser. $\endgroup$ – celtschk Oct 2 '14 at 17:55
  • $\begingroup$ An X-ray or gamma-ray laser may have the disadvantage that it would pass through material that it was intended to damage. Energy would not be delivered to a small volume. $\endgroup$ – Neil Slater Oct 2 '14 at 20:45
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    $\begingroup$ @DavidZ: The behaviour is very different when you get to that sort of energy. AFAIK, all substances are translucent to gamma rays, depending mostly on their density. $\endgroup$ – Neil Slater Oct 3 '14 at 8:30
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    $\begingroup$ Hey, added bonus: now you can fry all the members of the crew, and leave ships (mostly) intact! $\endgroup$ – ArmanX Oct 7 '14 at 16:25
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While the other answers point toward higher frequency radiation (and I agree with them) its interesting to note that Rayleigh scattering and other effects seem to point to the solution being opposite in an atmosphere, especially with particulates, due to bloom. Which, if I'm correct on that, has interesting implications in the event of planetary invasion as you probably would have sides with different colors. The atmosphere based troops would have redder while the space one's would have bluer to take advantage of their own tactical position.

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Colour, of course, has little to do with laser weapons. Movies and tv use different laser colours so us poor benighted viewers can know whose shooting who. The good guys' lasers are purple and the bad hats is yellow (for example).

Again colour would have little to do with most effective space combat laser weapons. The laser weapons would be operating in the x-ray spectrum for optimal destructive power. The reason why is simple. The wavelength of x-rays is effectively the same as the inter-atomic distances of solid matter. An x-ray laser beam weapon would be almost perfect at destroying spacecraft hulls.

This doesn't mean developing x-ray laser weapons is a certainty. There are formidable technical problems to be overcome and solved first. These may be the weapons of the not so near-future. But if they could be built, they would be the weapons of choice for space combat.

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The most powerful colour of light is nothing. As in the most powerful laser beam, would be something that you can't actually see. It is after all, the kind of light given off by the most powerful energy source, fusion, from stars.

Now if you're talking about particle weapon, that's a whole lot easier to say. Depending on the particles you use, it can be red, blue or yellow. And they're a lot more powerful than plain laser beams too.

I may be wrong about this, as I have only heard about it. But basically, ionized iron will appear as a red beam, ionized hydrogen will appear as a blue beam. Ionized hydrogen can also be pointed at the exact same spot on the target to create miniaturized nuclear fusion reaction. Ionized iron will probably be corrosive? Not quite sure about the iron.

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  • $\begingroup$ This is incorrect. "Nothing" isn't a color and stars don't emit just one color. White light is what you're thinking of, which is the combination of several wavelengths of visible light. $\endgroup$ – Frostfyre Jan 4 '17 at 13:20
  • $\begingroup$ Lasers use photons, not particles. Lasers are photons (which are also waves, due to wave-particle duality) that are 'coherent.' Coherent in the physics/optics sense means that they have a constant phase difference and are at the same frequency. By ionizing a certain ion, you can ensure that all photons released are the same frequency, due to the quantized nature of an ion's electrical states. The 'beam' of the laser itself does not consist of these particles. You should read up on laser physics before you try to answer questions about it. $\endgroup$ – kingledion Jan 4 '17 at 13:34
  • $\begingroup$ "I have only heard about it", can you provide a source? $\endgroup$ – Vincent Jan 4 '17 at 15:37

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