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[Rolepgeek]

There could be materials that degrade into reflective surfaces, you know. Also, if you can make explosions at the target site, why are you bothering with trying to burn through? The shockwave alone should incapacitate them.

Though range is a difficult thing to get right with those explosions. *shrug*

[Culise]

Dual beam colimation would make the "it's reflective silly!" argument go away.

Basically, when two beams of sufficient energy intersect, the local energy is sufficient to bloom the atmosphere at that point, making a small thermal explosion. You can damage even reflective surfaces with the resulting plasma ball that way. Once the surface is marred by this explosion, traditional beams will burn right through.

Now with video!
https://www.youtube.com/watch?v=1HHJhpStza0

As a corollary to this, you also have to worry about reflection efficiency.  Even if you assume 100% reflectivity at the particular wavelength of the laser on the part of the material itself, you have to worry about the angle of incidence, polarization, and the like.  Heaven help you if your armor ever gets a speck of dust or, worse, a scratch; any imperfections will absorb even more energy, reducing reflectivity further and causing even more energy to be absorbed from the laser.  While perfect mirrors do exist even today, in addition to the above, with these you also have to worry at high energy levels that any thermal bloom might cause a break between layers - another imperfection to cause rapid energy absorption and, again, catastrophic failure.  When you're talking about kJ or MJ of energy impacting something as fragile as a mirror, even a 0.1% absorption is not something to scoff at.

That is, unless you posit some material that somehow degrades into an even more reflective material, as rolepgeek did.  While I'm no expert, I'm afraid I've never heard of any such thing; I apologize, but could you give an example of something that exhibits this sort of behaviour, or is it simply a hypothetical on par with dilithium as a prerequisite for FTL travel?

[HAMMERMILL]

Maybe the armor material could vaporize into something that blocks or reflects light to diffuse the laser beam.

If the beam causes an explosion on the surface, any kind of armor will do since concussive shock-waves do a very poor job of penetrating conventional armor.

I think if the target were individual infantrymen wearing armor, a microwave weapon would work better. Lasers make more sense for anti-aircraft in my mind.

[wierd]

If the material volatizes under the beam, the beam will burn through. The issue of the beam being blocked by the volatized material is another of the many reasons why weaponized lasers are pulse lasers, and not sustained lasers. The gas cloud produced by the beam interaction disperses in atmosphere, then the next pulse hits, burning more away.

Reflective surfaces would avoid absorbing the energy of the laser, and thus avoid heating, and vaporizing. However, imperfections in the surface would cause the surface to absorb some of the energy. That's what the small plasma explosion does-- it mars the surface slightly through oxidation, and other high energy chemistry, caused by the breakdown of the atmosphere just at the surface of the material. this "coating" then absorbs energy from the laser, heats up, and vaporizes part of the reflective armor, allowing the beam to continue to chew through.

You need a magic material that is able to rapidly absorb the energy directed at it, and disperse it as diffuse thermal energy out of a large radiator of some kind.

[HAMMERMILL]

that is able to rapidly absorb the energy directed at it, and disperse it as diffuse thermal energy out of a large radiator of some kind.

Perhaps a plate of armor that is finely layered with different materials. Something shiny that reflects energy and something that vaporizes into something with a low thermal conductivity and maybe a third layer that vaporizes copious amounts of something opaque. Laser pulses, eats through the various laser it's energy its both reflected and obstructed by vaporized material and the thermal energy on the target dissipates and cools through the vapor. That way the vapor not only diffuses energy but also acts as a heat sink away from the target.

Maybe ceramic and chromium-alloyed layers. Not a material scientist though.

[Rolepgeek]

Metals can have their topmost, oxidized layers scoured away, leaving shiny insides. Principle of it seems sound, especially if it reacts to the wavelength of light to change configuration to be more reflective. I mean, nothing's gonna be perfectly reflective, but with good heatsinks, it just has to prevent a penetration. Superconductor armor is alsoan idea for this, as the heat of the laser would be spread over the entirety of the connected armor plating, and dissipate fairly quickly into atmosphere.  Add heatsink backing and, well...good luck with that.
Ablative armor is also an option.

But yes, theoretical material. Not on par with FTP material theoretical, though, I would think.

And yes, changing the light wavelength is a thing, but you need static electron lasers for that. Also,  changing the focal length of the fish isn't necessarily easy; getting the bean focused at the right point could be difficult to get a good penetration. Beam pulses are also unlikely to hit exactly the same spot as previous in a combat situation unless specifically set up to do so like the 'splodey lasers, and pulse length(and therefore, to some extent, power) and rate are inversely correlated.

The gas cloud released would either do it's job of stopping that one pulse, and then you'd be aiming at a different point on the armor, or it would help reduce or stop the next pulse because you fired it quickly enough after the first that there wasn't time for the gas to dissipate.

[wierd]

One solution to the "Need different frequencies in a hurry" problem is to use a precision comb laser as the pump laser, with a rotating turret full of different secondary induction media.

https://en.wikipedia.org/wiki/Laser_pumping

A comb laser is a special classification of laser that has precise peaks at different frequency bands. They are typically used to make precise interference patterns with other laser light sources to better measure the frequency band of those other laser light sources (Say for instance, in laser spectroscopy.)

https://en.wikipedia.org/wiki/Frequency_comb

In this case, you use the tuneable nature of the comb to pump a wide assortment of secondary media, which can be swapped in and out with a mechanical action. This doesnt completely solve the problem, but it does give you a much wider frequency selection to choose from.

The idea here is to apply a strong electrical gradient to the medium, then cause the cascade using the comb laser pump. The electrical excitation current can be supplied by the container holding the medium cylinder, and generated by the laser's capacitor bank. The charge supplied is just under the threshold required to initiate lasing, and the pump just tips it to the point of going. Thus cycling the pump, pulses the laser.

[Rolepgeek]

That would be interesting. Expensive,  and the cycle might become predictable enough to allow advanced systems to adapt to it,  but by that point, static lasers are probably available. Biggest thing is gonna be the expense and space needed for it, if I'm understanding it correctly. Probably only practical for fixed or vehicular weapons. Still,  it's probably be significantly better at getting through most laser-specific defenses. Be kinda like equivalent of AP rounds.
Speaking of which, with that rotating turret idea; what about gatling lasers? Each barrel might contain focusing equipment for different focal lengths and frequencies, designed so the focal points create a line reaching out from the firer along typical combat ranges. Firing also shouldn't overheat the equipment as easily, allowing for more readily sustained fire. If barrels are individually changeable, could even be modified to fit expected operational requirements; could make it an explosion generator as well if each barrel fires twice in extremely rapid succession (I think it can be the same laser firing to make it, right?).

So...lasers have HE and AP settings now. Huh.

[Amperzand]

I'm not sure if the term "Barrel" applies to a laser. They're generally pretty integrated.

That said, the sci-fi weapon it most makes sense to create a gatling variant of is a railgun, since the individual barrels don't last very many shots, and that number goes down rapidly if you fire them while they're still warm. It wouldn't really be the kind of rapid-firing weapon you usually associate with gatlings, but it'd work pretty well, and stave off needing to manually replace the multi-ton barrels every six shots.

[Rolepgeek]

I'm not sure if the term "Barrel" applies to a laser. They're generally pretty integrated.

That said, the sci-fi weapon it most makes sense to create a gatling variant of is a railgun, since the individual barrels don't last very many shots, and that number goes down rapidly if you fire them while they're still warm. It wouldn't really be the kind of rapid-firing weapon you usually associate with gatlings, but it'd work pretty well, and stave off needing to manually replace the multi-ton barrels every six shots.

For non-turreted weapons, such as handheld ones, and to make the most of the strategy I was envisioning, they would need barrels. Long pointy bits also make it easier to aim that the massive parabolic mirrors, for human operators.

[HAMMERMILL]

I'm not sure if the term "Barrel" applies to a laser. They're generally pretty integrated.

That said, the sci-fi weapon it most makes sense to create a gatling variant of is a railgun, since the individual barrels don't last very many shots, and that number goes down rapidly if you fire them while they're still warm. It wouldn't really be the kind of rapid-firing weapon you usually associate with gatlings, but it'd work pretty well, and stave off needing to manually replace the multi-ton barrels every six shots.

I read one sci-fi setting where lasers have 'barrels' that are just shields to help protect the lens from battlefield damage.

I think that guy means that the 'barrel' is a discrete laser weapon, just of a different type that's mounted on the same weapon system.

[Rolepgeek]

...I mean that the primary laser power source and/or pump is in the main body of the gun, with barrels mounted on that include a bunch of focusing equipment to allow for a smaller lens with a farther focal length than otherwise possible, as well as cooling mechanisms and adjusters/mediums to adjust the frequency to different levels.

[wierd]

Could also be the amplification medium itself as well.

[MonkeyHead]

I need to ask a question that'll make you think I'm stupid. That's because I'm stupid.

Is a low heat conductivity more important than high melting point? What if I layered something beneath the armor to absorb the heat?

If your armour conducts too much heat through it, whoever is inside it will get cooked. If its melting point is too low, it wont prtect much at all. You want both...

Absorbing the heat, if you have no way to dissipate it in some way, will lead to cooked wearer syndrome. The easiest way to dissipate it would be to conduct it away, presumably into some kind of heat sink system.

[Dansmithers]

Huh...

Apparently "beryllium [is] the metal with the best heat dissipation". So... should I go with a version of that?

Only if you want your grunts to get lung cancer