Physical model for strong optical-amplitude fluctuations in a turbulent medium

Tatarskii’s geometrical-optics model of scintillation has been generalized to include both diffraction and the loss of spatial coherence of the wave as it propagates through the turbulent medium. An estimate is obtained of the amplitude fluctuations that agrees with the results of perturbation theory for σϒ2⪡1 and saturates to a constant value of the order unity for σT2⪢1 ( σT2 is the amplitude variance calculated on the basis of perturbation theory). In addition, we have calculated the amplitude correlation function. For σT2⪡1, the amplitude correlation function agrees with the results of perturbation theory and for the Kolmogorov spectrum is characterized by a correlation length of the order (L/k)1/2, where L is the propagation distance and k is the optical wave number. Conversely, for σT2⪢1 the amplitude correlation length decreases with increasing propagation distance and is shown to be equal to the lateral coherence length of the wave ρ0(L). In this regime, a residual correlation tail is obtained in agreement with recent experiments.