In general, at the power levels in question the limiting factor is diffraction, not beam quality. There are a lot of variables going into it, but the numbers I'

In general, at the power levels in question the limiting factor is diffraction, not beam quality. There are a lot of variables going into it, but the numbers I've seen bandied about for orbital systems are on the order of 100km. See e.g. here: https://www.sciencedirect.com/science/article/pii/S1000936114001010 https://www.sciencedirect.com/science/article/pii/S100093611... (Or, for a more speculative take, here: https://childrenofadeadearth.wordpress.com/2016/07/02/the-photon-lance/ https://childrenofadeadearth.wordpress.com/2016/07/02/the-ph...)