Optical EngineeringScintillation in ground-to-space and retroreflected laser beams
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In the Relay Mirror Experiment (RME), three laser beams were propagated from ground to space and retroreflected from the RME spacecraft. An argon-ion beam at 488-nm wavelength and a Nd:YAG beam at 1064-nm wavelength were projected from a site at an altitude of 3050 m and an argon-ion beam at 514-nm wavelength was projected from a site 20 km away and at an altitude of 100 m. The beams had divergences ranging from 30 to 90 μrad. Uplink irradiances at the spacecraft and the retroreflected irradiances at the ground were measured. The data indicate that the uplink scintillation varies significantly within the Gaussian profile of the beams, and that the uplink scintillation is dominant in the retroreflected beams. The temporal spectrum of the scintillation shows a sharp roll-off beyond a characteristic corner frequency. The corner frequencies observed ranged from 400 to 700 Hz. The implications of the strength and temporal nature of the scintillation on fade statistics of the retroreflected beams are discussed.