Optical communications – over the horizon (NLOS)
The DX record for communications at optical frequencies is phenomenal these days. There is a growing interest in communications over non line of sight paths (NLOS) using cloud-bounce or clear air scattering. To my knowledge, in recent times experiments are (or are about to start) by F1AVY, VK4EBP , VE7SL and G3XBM (when fit again). I am sure there are others too. Weak signal modes certainly help. I used QRSS3 over an 8.5km NLOS path, but much further has been achieved.
Australian Optical DX https://groups.yahoo.com/neo/groups/Optical_DX/info
This is interesting. You got me wondering about an optical Moonbounce program, since it has been done numerous times with high powered and very sensitive–read expensive–equipment. I bet some bright hams could devise a program to reduce the cost of gear that could pick up a signal, but building a kW laser that could do the job would be tremendous challenge. It would be quite a technical achievement, though.