30, 20, and 10 Years Ago in OPN

“Atmospheric compensation may be accomplished using bright stars but, unfortunately, complete sky coverage is not possible with the limited number of bright natural guidestars. To solve this problem, a synthetic beacon (or laser guidestar) may be created either by reflection from nitrogen and oxygen molecules in the lower atmosphere (Rayleigh scattering) or by resonant backscatter from a layer of sodium atoms 90 km above the earth … Researchers at MIT Lincoln Laboratory were first to demonstrate real-time correction using a laser beacon and deformable mirror.”