Validity of using Gaussian Schell model for extended beacon studies

In many military applications that use Adaptive Optics (AO) a point source beacon is ideally required at the target to measure and to correct for the wavefront aberrations caused by propagation through the atmosphere. However, it is rarely possible to create a point source beacon at the target. The "extended beacons" that are created instead have intensity profiles with a finite spatial extent and exhibit varying degrees of spatial coherence. The Gaussian Schell model might be a convenient way to model these extended sources because of its analytical tractability. The present work examines the validity of using such a model by evaluating the scattered field from a rough surface target using a full wave electromagnetic solution (method of moments). The full wave electromagnetic calculation improves the fidelity of the analysis by capturing all aspects of laser-target interaction i.e. shadowing/masking, multiple reflections etc. A variety of rough surface targets with different roughness statistics has been analyzed. This analysis will ultimately aid in understanding the key parameters of extended beacons and how they impact the Adaptive Optics (AO) system performance.