Study On Unstable Laser Resonator Alignment Methods Based On Fringe Pattern Processing

The cavity mirrors alignment of the unstable resonator in a high-energy laser has direct influence over the quality of its output beams and the stability of its output power. Therefore, it is necessary to align the cavity mirrors before each operation. The near-field patterns of the guided light of the unstable resonator present themselves in the form of interference fringes. And their distribution shape has some direct relationship with the cavity mirrors' misalignment. Based on this, the artificial cavity mirrors alignment has been realized and applied widely. However, the existing approach has inevitable disadvantages of limited alignment precision, long time consumption, and poor repeatability in actual construction. To solve these problems, a resonator alignment method based on fringe skeleton processing and a resonator alignment method based on the fringe pattern grey projection were proposed,and also the experimental study were carried though.In this thesis,based on a systematic introduction of existing cavity mirrors alignment methods, we focus on positive-branch con-focal unstable resonator, which is one of the most common resonators of high energy-laser as an example, analyzed its structural features and offset characteristics, and further discussion of the output near-field interference fringes of guide light's formation mechanism and the relationship between the distribution shape of interference fringes and the offset amount of cavity mirrors, proposed a resonator alignment method based on fringe skeleton processing and a resonator alignment method based on the fringe pattern grey projection, and also established corresponding objective criteria of cavity mirrors alignment degree, wrote the cavity mirrors alignment degree analysis software, built experiment platform of the two cavity mirrors alignment methods. Results show that the resonator alignment method based on the fringe pattern grey projection's image processing speed and processing accuracy are much better than the resonator alignment method based on fringe skeleton processing, The former method can do real-time image processing and analysis, it's calculation error is less than 0.1 pixel. In addition, the experiments also prove that: with the aid of fringe pattern projection method, the artificial cavity mirror alignment method can effectively improve it's alignment accuracy, To achieve an accuracy better than 15.7μrad.