Rayleigh-Ritz optimization of the structure function for a Kolmogorov power density and an approximate analytical solution for the two-point electric field correlation function.

Beginning with the exact Kolmogorov power spectrum for an extended random medium (such as interstellar space), the structure function is first expressed as an inverse Fourier-Bessel transform. An approximate series representation involving fractional powers of the transverse coordinate is then optimized by an equivalent Gaussian expansion up to two terms using the Rayleigh-Ritz technique. The domains of validity as well as the coherence profile of the resulting analytical solution of the two-point electric field correlation function are examined. It is shown that the correlation in both the transverse and longitudinal directions persists over distances up to a few orders of magnitude greater than that for a medium described by a Gaussian structure function.