| Brightness of artificial beacon is a critical factor that restricts the adaptive optics system's performance on observing astronomical targets.Traditional solutions are usually limited by hardware performance.Therefore,our group proposes an approach that enhancing the weak artificial beacon by nonlinear effect.It aims to amplify the wavefront in amplitude when its phase information is maintained.This paper mainly focus on the divergence feature and multi-frequency lasing characteristic of the near-degenerate second-order nonlinear output in order to understand the influence brought by the nonlinear process better.The main contents of this thesis are shown as follows:1.Basing on the application background,optical parametric amplification,the beam carrying orbital angular momentum and its nonlinear frequency transformation,etc.a novel scheme for wavefront detection has been proposed.2.In the degenerate QPM optical parametric process,the divergence feature of the tightly focused pumped PPLN output are studied.The evolution trait of output spot and spectrum varied with temperature are summarized,and this phenomenon can be explained by temperature-induced phase-mismatching.Similar phenomena obtained under various experimental conditions also indicate that this feature is ubiquitous.3.The multi-frequency lasing characteristic of the second-order nonlinear process is studied in both non-degenerate and degenerate QPM dual-seed non-collinearly injected optical parametric amplifier.In the experiment,both the frequency interval and the lasing frequency amount of the multi-frequency lasing could be flexibly controlled,and these phenomena can be explained by the cascaded second-order nonlinear effect.4.Based on spatial light modulator,vortex phase plate,laser cavity and other methods,the experimental exploration of generating orbital angular momentum beam is carried out,and the improving measures for generating the orbital angular momentum beam are proposed. |
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