Since the 1970s, researchers working first for the Defense Advanced Research Projects Agency and later under the aegis of the Strategic Defense Initiative have been developing and testing adaptive optics systems—systems for nullifying the effects of atmospheric turbulence on light that passes through it. In May 1991, to the delight of the astronomical community, much of the work became declassified. Adaptive optics works by measuring the distorting effects of the atmosphere on the light from a guide star and adjusting a deformable mirror to conjugate these effects. In particular, the declassified research involves the use of laser beams to create one or more artificial beaconsin the sky to act as guide stars.
Graham P. Collins; Making Stars to See Stars: DOD Adaptive Optics Work is Declassified. Physics Today 1 February 1992; 45 (2): 17–21. https://doi.org/10.1063/1.2809522
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