Intracavity adaptive optic compensation of phase aberrations III: Passive and active cavity study for a large N_eq resonator

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Abstract
The results of a numerical study of both the passive and the active mode-structure properties and far-field behavior of a linear, positive-branch, confocal unstable resonator with a large equivalent Fresnel number in the ideal unaberrated, intracavity phase-aberrated, and intracavity phase-corrected states are presented. A simple, saturable, gain-medium model of a homogeneously broadened CO2–electron-beam discharge laser system is employed in the active cavity study. The active cavity results presented here show that, at least for the level of gain saturation considered, the passive cavity theory of phase-aberration sensitivity remains applicable in this more-physical situation. Furthermore, the ideal correction to phase-tilt and curvature aberrations, derived from passive cavity considerations, remains exact in the presence of saturable gain. Finally, the influence of a multidithered, zonal deformable mirror on the cavity-mode structure and far-field behavior is analyzed in order to account for recent expe imental tests of the intracavity adaptive optics concept.