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Chapter 5:
Aiming and Focusing Optical Beams through the Turbulent Atmosphere
In problems of optical sounding, communication, and energy transmission one frequently runs up against the problem of transporting radiant energy in the form of a light beam to an object located in a random inhomogeneous medium. Here, as a rule, it is necessary to maximiz.e the amount of energy delivered to the object. As is well known, scattering of radiation by refractive index inhomogeneities of the medium leads to a decrease of the average intensity in the near-axial region of the light beam and to the appearance of intensity fluctuations, which taken together substantially degrade the energetic characteristics of the indicated systems. A radical means of dealing with these undesirable effects is to use various adaptive methods which allow one, at least in principle, to almost completely eliminate the influence of the inhomogeneities of the medium. Essentially these methods control the initial distribution of the beam field on the basis of information about the instantaneous distribution of inhomogeneities of the medium in which the beam is propagating.
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