On the Phase Structure and Mutual Coherence Function of an Optical Wave in a Turbulent Atmosphere

Abstract : The present work shows that the most commonly used expression for the mutual coherence function (MCF) for an optical wave propagating in a turbulent atmosphere is, in general, incorrect. This expression is based on an unphysical extrapolation of the Kolmogorov spectrum. Along an atmospheric path, with specified turbulence parameters, the new MCF is shown to imply greater resolution, less beam spreading, and greater heterodyne signal-to-noise ratios than indicated by previous calculations. By comparing these results with those previously obtained for heterodyne detection, the percentage errors in the previous calculations are shown to increase with decreasing propagation paths. In particular, where it was formerly thought that the atmosphere limited the effective coherent detection size in heterodyne detection at all ranges, the present calculation reveals that over sufficiently short paths, there is no size limit imposed by the atmosphere.