Correlations of photon trajectories in the problem of light scintillations

A distribution function approach is applied to describe the dynamics of the laser beam in the Earth atmosphere. Using a formal solution of the kinetic equation for the distribution function, we have developed an iterative scheme for calculation of the scintillation index ($\sigma^2$). The problem reduces to obtaining the photon trajectories and their correlations. Bringing together theoretical calculations and many-fold computer integrations, the value of $\sigma^2$ is obtained. It is shown that a considerable growth of $\sigma^2$ in the range of a moderate turbulence is due to the correlations of different trajectories. The criteria of applicability of our approach for both the coherent and partially coherent light are derived.