Wavelengths of laser weapons

[VoxRationis]

Does anyone know what wavelengths are used for prototype laser weapons? I'm trying to calculate maximum effective range for laser weapons in space, in order to design a game.

[HandofShadows]

Simple green for the good guys red for the bad guys. :smallbiggrin:

Really though, lasers are light. The wavelength difference between the different colors it very slight and really not enough to effect range in space. (water or the atmosphere is a different subject!) In space the important thing is the ability to focus the beam at long ranges. For instance if you fire a laser from the Earth to the Moon when it arrives at the moon it covers the bigger than a football field.

[Brother Oni]

Does anyone know what wavelengths are used for prototype laser weapons? I'm trying to calculate maximum effective range for laser weapons in space, in order to design a game.

I don't know about prototypes, but there is a functioning laser weapon already deployed - the LaWS on the USS Ponce. Admittedly I can't find a wavelength value (presumably because it's classified), but I've found numerous articles indicating that it's six 5.5 kW solid state electric fibre lasers (thus most likely in the 1000+ nm wavelength range), incoherently combined to output 33kW.

This article explains it better: link (http://www.laserfocusworld.com/articles/print/volume-48/issue-04/features/the-state-of-the-art.html).

There's also this PDF on US Navy weapons research: link (https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwjL_bPhmNzJAhWC8RQKHeUhBVoQFgguMAI&url=https%3A%2F%2Fwww.fas.org%2Fsgp%2Fcrs%2Fweapon s%2FR41526.pdf&usg=AFQjCNG8IW4Svr-XRsFKBvA2UjCAxbWymA&sig2=Y0LqD8_XnMf6aIDAukeSsA&bvm=bv.109910813,d.d24).

[VoxRationis]

Simple green for the good guys red for the bad guys. :smallbiggrin:

Really though, lasers are light. The wavelength difference between the different colors it very slight and really not enough to effect range in space. (water or the atmosphere is a different subject!) In space the important thing is the ability to focus the beam at long ranges. For instance if you fire a laser from the Earth to the Moon when it arrives at the moon it covers the bigger than a football field.

Isn't that focusing ability dependent on wavelength?

[HandofShadows]

Isn't that focusing ability dependent on wavelength?

Yes, it would. But only in a minor way. The wavelength of light is very small compared to the whole spectrum of radiation. If you where comparing Lasers to X-Ray lasers there would be a larger difference.

[Seppl]

Yes, it would. But only in a minor way. The wavelength of light is very small compared to the whole spectrum of radiation. If you where comparing Lasers to X-Ray lasers there would be a larger difference.The visible spectrum does not define the possible wavelengths of laser weapons. Calling something a "laser" or "maser" or "x-ray laser" or something else is just a different word for the same kind of device. In everyday language all these devices are called "laser", no matter if they operate in the visible spectrum or not.

You would actually prefer a shorter wavelength for a weaponized laser. It is very inefficient when 90% of the beam's energy can be deflected by a shiny metal surface. Contemporary laser weapons (which work in the micron range, thus infrared) can only be used against targets where even these 10% can quickly melt the surface (which then usually increases adsorption for the rest of the burst) and where the adsorbed energy is sufficient to actually do damage to anything below the surface.

On the other hand, a hypothetical high UV- or X-ray laser would immediately disrupt the very bonds that hold matter together. Which is one of the reasons why it is very hard to build a laser (much less a powerful one) for these wavelengths.

[Siosilvar]

As always, GGG3 and Atomic Rockets (http://www.projectrho.com/public_html/rocket/spacegunconvent.php) are good sources for this sort of thing. Not perfect by any means, but a fairly plausible simulation.

GGG3 lists effective damage of lasers for game purposes as sqrt(0.735 * energy (J) / radius (mm)). For comparison to conventional rounds, 9x19mm is around 20 damage, 5.56 NATO is around 50, and 12.7mm is around 100 (120 for ADPS rounds). I wouldn't consider anything less than 500 or so suitable for space combat.

Atomic Rockets lists radius at target equal to 0.61 * distance (m) * wavelength (m) / radius of lens (m).

So, shorter wavelengths, closer distances, and bigger focusing apertures are better, as expected (but each has its downsides). Effective range will depend on all of these and how much power you put into the laser. Though with a big enough laser, your targeting data becomes more of a limit on your range than your weapons are.

[Gray Mage]

I think that for space battles the aiming system accuracy is more relevant to a max distance than the laser's focus.

[Caesar]

Current weapons-grade systems have an effective range, in atmosphere, of about 1 mile, as reported by the US Navy. In space you are going to extend this considerably, as scattering is no longer an issue. You will always have two problems tho, beam divergence and beam coherence length, which are impossible to perfect due to quantum limitations on any system. Simply put, the uncertainty principal will always give you an imperfect beam that spreads out over time.

That said, who cares? Its a work of fiction, your lasers work in the most interesting way you need for the game to remain fun. Nobody wants to do doctorate level physics calculations when they are rolling to hit, let alone damage (and by the way, what you are aiming at is just as important as what you are aiming with).

[Lorsa]

The maximum effective range is very very far away. All you need to do is make sure to focus your beam at the location of the ship you want to fire at. As far as I know, that is only a lens issues, but if you're already in space, that shouldn't be a big problem.

[Brother Oni]

Nobody wants to do doctorate level physics calculations when they are rolling to hit, let alone damage (and by the way, what you are aiming at is just as important as what you are aiming with).

Unless you're playing Rolemaster or Traveller. :smalltongue:

[VoxRationis]

Current weapons-grade systems have an effective range, in atmosphere, of about 1 mile, as reported by the US Navy. In space you are going to extend this considerably, as scattering is no longer an issue. You will always have two problems tho, beam divergence and beam coherence length, which are impossible to perfect due to quantum limitations on any system. Simply put, the uncertainty principal will always give you an imperfect beam that spreads out over time.

That said, who cares? Its a work of fiction, your lasers work in the most interesting way you need for the game to remain fun. Nobody wants to do doctorate level physics calculations when they are rolling to hit, let alone damage (and by the way, what you are aiming at is just as important as what you are aiming with).

I just want to establish a good baseline weapons range for the design phase. No laser range calculation will be necessary in-game.

[Lorsa]

I think you can safely assume your laser weapon range to be equal to your sensory / distance determination range. Or ibainite if you so desire.

That is, unless you want to include power output in the equation, if that becomes a factor then things may get difficult. Assuming you spaceships can crank out pretty much any power levels, range will not be a factor.

The problem is in the targeting, as you need to know exactly where to focus the beam. This requires other techniques, and clever guessing by the shooter as to how the other ship will have moved in the minutes or hours it takes for your laser weapon beam to arrive.

[Caesar]

Lorsa, you are missing some important points about lasers. First, they come out of the cavity almost parallel by definition (there is some inherent spreading caused by quantum mechanics as well as imperfections in any laser mechanism). You could focus it to a point downstream, but that is not something that will be easily done in short time to cover a large range of possible distances. Furthermore, when you introduce a lens into the beam, it spreads the beam out according to the energy spread in the beam (no laser is perfectly monochromatic), which drastically reduces the power of the beam because now you cant actually focus to a point, you have induced a chromatic aberration. Finally, there is a coherence length which says that the photons of slightly different energies will only remain in phase for a specific amount of time(distance). Once they are out of phase, they begin to destructively interfere with each other as bosons are want to do, and you end up with again, less power at the end point. A lens also destroys coherency.

So the end result is that even a really great, nearly perfect laser will spread out and lose energy through various mechanisms, such that it is useless as a weapon after a given distance. And putting a lens into the beam just makes things worse.