主题：大家觉得美国登月是不是个骗局 -- 华虎

first of all, for this kind of ranging systems, laser is never directly shot into the air naked, there is always an optical lens system in front. for lunar laser ranging, they use a telescope. so the characteristics of the telescope decide the beam divergence. it does not make any sense to talk about beam diameter when laser hitting the moon without talking about what kind of telescope or during which experiment.

the 6km (actually closer to 7km) diameter number is specific to the telescope used by the mcdonald observatory station, one of primary stations used in lunar laser ranging experiments, a 2.7 meter reflecting telescope.