[jjtheblunt]

would the atmosphere along the beam path vaporize in short order at those power levels, so scattering/attenuation is temporary for a fixed beam?

[nine_k]

If it does so, the resulting plasma will very actively absorb the laser pulse's energy.

Your best bet is not interacting with the atmosphere in any way, and merely adjusting for refraction.

[akiselev]

Maybe, maybe not; self focusing [1] is an active area of research. Optics is one area where secret projects have been shown to be way ahead of what is publicly available [2] so I wouldn't be surprised if they've figured out some scifi way of making orbital lasers more effective.

[1] https://en.wikipedia.org/wiki/Self-focusing

[2] https://en.wikipedia.org/wiki/2012_National_Reconnaissance_O...