Numerical analysis of mode properties for confocal unstable resonators with intracavity astigmatism-aberrated perturbation

For a laser resonator cavitiy using an unstable resonator configuration, experiments have proved that the intracavity perturbation is an important influencing factor for degrading the output energy and the beam quality. The influence on eigenmode properties for passive unstable resonators has been analyzed. The effect of the intracavity astigmatism-tilted perturbation on the mode properties for positive-branch confocal unstable resonators has been calculated numerically by using an iterative method. The phase structure of the output beam is analyzed by adopting the Zernike mode-reconstruction theory; and Zernike aberration coefficients of the first 35 order, integrated relative far-field intensity, and point spread function(PSF) are all obtained. These numerical results illustrate that sma