Linear propagation performance in high power laser facility

The diffraction character is redefined based on Fresnel number. This new definition is extended to focusing or diffusing optical path. The sign of the new diffraction character is defined for each optical element in a laser system. According to these definitions and extending, the effect of phase aberration on near-field modulation and the effect of linear diffraction on FM-to-AM are studied. The linear diffraction effect on high power laser facility can be evaluated by the combination of the new diffraction character and the energy fluence.