Free space optical system *intentionally" spread the laser beam using a lens. The light beam still consists of parallel rays, and when they hit the receiving lens they focussed again on the receiving diode (or whatever sensor). The idea is to accept that the beam will be disperse in the air, or due to variation at the transmitter, but still to catch enough of the transmission. https://en.wikipedia.org/wiki/Free-space_optical_communicati...