I would think that you’d need a lot of energy produced to destroy an aircraft. Granted,you could pack a lot of generators on a ship but you would probably be limited to short bursts. Maybe the way they’re destroying them is by making the onboard sensors inoperable. Also you’d have to be relatively close to the target. I’m not sure if the inverse square law of light applies to lasers. Maybe a photon torpedo would be better.
No. Inverse square applies to an omni-directional source.
There is some spread of the beam and atmospheric losses even on a clear day, of course...
No, the inverse square law does NOT apply to lasers. That is why they even work at all. Lasers do spread, but not that way.