Beam quality analysis of solid-state zigzag tube lasers for long-distance propagation in atmosphere

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Solid-state zigzag tube laser (SSZTL) is a new type of solid-state laser source with structural compactness, high gain, as well as direct transmitting. To solve the problem that the beam quality of the tube laser significantly degrades during long-distance propagation in atmosphere, the method for improving the beam quality of the tube laser based on the right-angle conical deformable mirror have been proposed. The beam correction model and the beam propagation model in atmosphere of the tube laser have been built up and the beam quality of the tube laser after long-distance propagation in atmosphere have been analyzed. Firstly, a scheme for obscuration ratio transformation of annular tube lasers have been provided, based on which the matching of the small-aperture large-obscuration-ratio tube laser and the large-aperture small-obscuration-ratio Cassegrain system have been accomplished. Then, the impacts of the beam quality of the tube laser source, the atmosphere turbulence effect and the thermal blooming effect on the propagation characteristics of SSZTLs have been numerically studied, and the mechanism of the beam quality degradation of the tube laser in the procedure of the long-distance propagation in atmosphere have been revealed. To improve the beam quality of the tube laser in far field, the right-angle conical deformable mirror have been used to correct the aberrations of the tube laser source and the phase distortions induced by the turbulence and thermal blooming effects in atmosphere. The results show that the beam quality of the laser source have been significantly improved after correction. Also, the Strehl ratio in far field have been obviously improved, especially used together with conventional deformable mirror.