What kinds of lasers are there?
There are a lot of different types of lasers, but the only ones that have been seriously studied for military useage in real life are chemically powered lasers, and solid state lasers.
What's the difference?
Power source. Chemical lasers are powered by a chemical reaction, solid state lasers require electrical energy. Chemical lasers (currently) have a generally higher output, but solid state laser technology (such as the products of the United States' Joint High Power Solid State Laser program) are significantly smaller, making them better for mobile applications. They also have lower output, but this is seen by most people involved in the field as an engineering issue, rather than something insurmountable. In other words, solid state lasers are the wave of the future, but the technology for chemical lasers exists right now. I mention both because some people may have a stricter definition of MT than others.
It should be noted that solid state lasers have a bulky power supply as well, but this power supply is also usually going to be the engine of whatever they're mounted on it for the most part, so you arn't going to need as much of a separate power supply. Research continues to miniturize important components!
A caveat: not all of the power supply is the engine. Some of it is going to be the components that turn the raw juice into stuff the laser needs.
How do lasers hurt things?
To quote Wikipedia, "The general idea of laser-beam weaponry is to hit a target with a train of brief pulses of light. The rapid evaporation and expansion of the surface causes shockwaves that damage the target."
In other words, a laser weakens and fatigues the structure of a target and basic physics does the rest. At least, any of the lasers you will see in MT will be working in such a fashion. And really most of the time that's all you'll need-- lasers that can vaporize huge chunks of a target are extravagant at best and likely to be primarily limited to ground-based installations.
Sounds pretty nifty. What are lasers useful for?
Primarily, anti-aircraft work. Specifically, aircraft, missiles, artillery shells and mortar rounds are all prime targets for lasers. On a larger scale, they're also useful for intercepting ballistic missiles and ICBMs, but that's rather outside the scope of this document, which is intended to discuss them as applied in a tactical fashion. In the future, sufficiently powerful lasers may allow damage and destruction of soft targets (eg things that arn't armored or arn't very well armored) from the air, but this is only in conceptual stages in real life.
Ha! I'll just put mirrors on all of my stuff. Then your lasers won't work!
This is actually a rather common misconception. First of all, not all lasers operate in the visible spectrum, which means that a given mirror won't be 100% effective against all lasers.
Second, a mirror needs to have 100% efficiency for this to work well, and no mirror operates at 100% efficiency. Even laser-grade mirrors-- eg mirrors as good as the ones used in the laser itself-- won't work for this, because they don't try to absorb the full power of the beam and are just used to focus it.
Third, shining a laser pointer at your bathroom mirror is rather an order of magnitude away from what happens with a combat laser-- at least 100 KW (assuming your laser doesn't suck) is being focused on a tiny area.
Assuming you've done something impossible and created the perfect mirror, it still won't work. Anything at all on a mirror-- water, bugs, dust, fingerprints, the ice that forms on aircraft at high altitudes-- will absorb enough energy to instantly vaporize with the first few pulses, transferring heat and distortions and vibrations to the mirror. The glass will crack and shatter (or the material will distort, if it's not made of glass), and the mirror at that point becomes useless.
Also, obviously enough, covering something mostly with mirrors will make it's radar cross signature larger, which means it will be less stealthy.
So much for mirrors. What about ablative coatings?
Ablative coatings, are, essentially, armor for stuff-- in theory, they'd be there to soak up the laser fire and burn away while leaving whatever they're protecting unharmed. Unfortunately, this is not really a useful solution on anything that has to fly, both due to weight concerns and due to how lasers work (as previously explained above). Armoring your big bad cruise missile sounds like a good idea, until you realize that a) it now has much less range, b) you can't armor every part of the body (control surfaces, sensors, intakes, etc), and c) due to how lasers do damage, as explained above, this won't work well on something that has to move quickly through the air anyways since it's own movement will cause it to tear itself apart or go off course. Also, obviously, the effectiveness of your ablative coating is directly related to how powerful the laser shooting at it is.
How about smoke?
Using smoke to defend aircraft and missiles (or, really, any moving object) against lasers is so obviously problematic that I'm not going to touch seriously on it.
Well, lasers sound pretty badass, but what are the limitations?
For chemical lasers, bulk, weight, and the need to haul large amounts of toxic chemicals around. For solid state lasers, power output; this is something that's being rapidly improved in real life, but even so, don't expect to see them installed in fighters for a few years at least. (next decade is probably a better guess for widespread deployment). Solid state lasers also have weight and size concerns, but not nearly as much so as chemical lasers; the F-35, for example, is projected to be able to use one. Fitting them in larger aircraft is not terribly difficult.
Also, more obviously, lasers only work in line of sight, so they can't hit things over the horizon.
How much of a problem is bad weather for lasers?
Rain, snow, and fog will all reduce the maximum range of a laser, but it won't make one completely useless. That being said, you should be backing up lasers with missiles in any case, so this is not as much of a problem as it sounds. Also, obviously, you can build a laser that uses a wavelength that's more effective at penetrating water, meaning that atmospheric moisture will scatter your beam less.
Furthermore, bad weather does not uniformly affect an entire area-- there are real life experiments with using a low powered laser to determine an optimal beam path and then firing when there's an adequate gap in the weather.
Is it possible to build a laser rifle?
Not in MT, and almost certainly not in PMT. It's just not possible to reduce the size of a laser and it's power source that much. And, frankly, there is no need-- human bodies are fragile enough that ordinary lead bullets will do fine.
How about one of those really cool lasers that shoot things from space that I saw in this one anime?
Space to surface lasers are silly for numerous reasons: a gigantic power source would be needed to pump a laser capable of hitting anything on the ground from orbit, and the laser itself would need to be quite powerful as well, as it would be punching through the -entire- atmosphere. So, no, not really practical at all.
How powerful does a laser need to be to engage a particular target?
You're in luck! There's been assorted studies done on this and here are the results:
Here's another image that provides similar information.
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This should answer most of the obvious questions; please suggest more below!
