Recently I have read an article about orbital mirrors, benefits and future applications of these devices. There was a figure which basically explains how divergence angle affects spot size on Earth. For example if you take the diameter of the mirror 100 meters and put it on 400 km LEO it would create a spot about 4 km diameter.
This example was based on an orbital flat mirror. The author also included two formulas for determining the spot area.
for a non-focusing reflector:$$A_{e} = A_{r}+\frac{\pi}{4}(\alpha h)^2$$ for a focusing reflector: $$A_{e} = \frac{\pi}{4}(\alpha h)^2$$
In the latter equation we still can not get rid of the divergence angle which is approximately 9.3 mrad. Is there a way to further narrow the spot size on Earth? I also looked at Gauissian beam and beam waist equations but could not totaly figure it out. Can you also include some calculations with your answers?