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Chapter 2:
Efficiency of Phase-Conjugation Optical Adaptive Systems
In the present chapter we will analy:ze the possibilities for correcting turbulent distortions of optical beams. We will examine the two limiting cases: the one in which the correction is based on a point reference source (beacon), and the one where it is based on a wide reference beam (Ω0→∞;), in the limit-a plane wave. The first of these is realized when both sources are located in the random inhomogeneous medium and their angular dimensions differ strongly [ka2 » (x1 - xo), ka02« (x1 - xo), equivalently Ω » 1, Ω0 « 1], and the second, when the reference source (of any geometry) is far enough removed from the layer of random inhomogeneous medium, and for which the reference wave is already a plane wave by the time it reaches the layer. We will also consider the dynamic characteristics of adaptive optical systems by defining the requirements on the system bandwidth and the case in which the wavelength of the main beam differs from that of the reference beam. We will use the phase approximation of the Huygens-Kirchhoff method to calculate the moments of the corrected field. As is shown in Appendices A and B, the random phase geometric-optics approximation can provide a quite effective description of the moments of the field intensity of the corrected optical wave.
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