When laser bcams are propagated through the air, they are modulatcd with a noise-like spectrum1,2having a baseband width the order of hundreds of cycles and a nearly exponential frequency distribution.1Hogg1used a 2.6-km path; Hinchman and Buck2used paths of 9 and 90 miles. In each case the optics alld range were such that the receiver col lected a small fraction of the total beam. Since atmospheric refraction causes twinkling and tearing of the beam, one would expect amplitude modulation of the signal received under these conditions even for constant intensity of the total beam.
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Subramanian et al. (1965) studied this question.
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