Simulating the effects of an extended source on the Shack-Hartmann wavefront sensor through turbulence

In this paper, we study a method of simulating optical wave propagation from a sodium laser beacon, specifically applied to Shack-Hartmann wavefront sensing. A Gaussian laser is propagated from the ground to the three-dimensional scattering volume in the mesosphere (80-100km). The resonant backscatter acts as the laser beacon for the adaptive optics (AO) system. This volumetric aspect is modeled by using multiple slices at different altitudes in the sodium layer. Weak turbulence is used in the experiment and the AO system is operated in the open-loop regime only. This paper investigates the number of slices required to adequately reproduce perspective elongation in the Shack-Hartmann spots. The study showed that the most stringent case in the simulations required nine evenly-spaced slices. Other ways of distributing the slices may lead to different results.