I would maybe make an inquiry to the Palomar Observatory. When driving to San Diego, I used to see blue lasers criss crossing the sky every once and a while. I'm not sure what they are aiming at, it is on a fairly horizontal trajectory, Local Mountains?
I would guess that it would have to be fairly powerful. Mucho megawatts! To have to go through 100,000 feet of atmosphere/dust, then 250,000 miles of space(solar wind), bounce then make the return journey and still retain a readable straight beam, requires a real highly energized beam of light. Just the dust in our atmosphere has a large light scattering effect, that's why the sky is blue when the sun is up.