Based On SPGD Optimization Algorithm Research On Auto-alignment Technology Of Positive-branch Confocal Unstable Resonators

Technique for automatic alignment of the resonators plays an important role in high energy lasers system automatization. If the mirrors of the resonators are misalignment, the high energy lasers will make the beam quality bad and reduce the output power, even produce severe ununiformity of intensity distributing. In this thesis, the technique for auto-alignment of positive-branch confocal unstable resonator that is one of the most common resonators of high energy lasers was investigated. Firstly, the typical approaches of auto-alignment of the unstable resonators are introduced,and the method that applies the stochastic parallel gradient descent (SPGD) algorithm to realize auto-alignment of the resonator is presented. Secondly, the characteristics of the passive positive-branch confocal unstable resonators are analyzed in theory. Then the auto-alignment system of the positive-branch confocal unstable resonators was set up and the system software based on SPGD control algorithm was accomplished along with selecting a suit system performance metric function that was applied to evaluate the alignment quality of the resonator, and at last the closed-loop control of automatic calibration of the misalignment resonator was actualized. The experiment results indicate that the method can realize auto-alignment of the misalignment resonators in the range of misalignment, which the range for tilt misalignment is from 0 to 170urad and the decentration range is from 0 to 1mm. The work of this thesis provides a new technical approach for a practicability high-power laser auto-alignment system.