Effect of spatial coherence on laser beam self-focusing from orbit to the ground in the atmosphere.

The effect of spatial coherence on laser beam self-focusing in the atmosphere to assist delivering powerful laser beams from orbit to the ground is studied. It is found that a fully coherent beam is more strongly compressed on the ground than a partially (spatial) coherent beam (PCB), even so, for a PCB the compressed spot size on the ground may be reduced below the diffraction limit due to self-focusing effect, and a PCB has higher threshold critical power than a fully coherent beam. Furthermore, an effective design rule for maximal compression without beam splitting of the transported PCB from orbit to the ground is presented.