The Research Of Deformable Mirrors In The Mcao System

In astronomical observations, the dynamic interference of atmospheric turbulence was discovered very early. It greatly affects the propagation of light, leading to unsatisfactory results of optical observations. To compensate for the turbulence disturbance, people gradually formed an idea, or precisely, a procedure to correct the wavefront aberration, that is, to detect the turbulence at first, then the control signal calculated by the computer could be sent to correct it. Afterwards the subject—Adaptive Optics(AO)—has eventually developed in view of the above-mentioned ideology.Although AO could correct the wavefront aberration to a great extent, there are still some limitations. Due to the impact of anisoplanatism, the field of view(FOV) will be restricted to a very small angle, which exerts a strong influence on observation results. Hence Beckers, who comes from the European Southern Observatory, proposed the Multi-conjugate Adaptive Optics(MCAO). The core of the method lies in: first, dividing the turbosphere into several layers; after that, a deformable mirror will be utilized separately for each turbulent layer to correspondingly correct the wavefront aberration caused by atmospheric disturbances.This article is aimed at probing into some main components of the MCAO system, especially the deformable mirrors. Many researchers, at home and abroad, have already carried out extensive research into deformable mirrors and even have built some prototypes. Thus, there is no lack of precedents in this connection. Regrettably, there are still some outstanding problems. Take Micro Electro Mechanical System(MEMS) deformable mirrors for example. It has been widely used for its low cost. Unfortunately, most commercial MEMS deformable mirrors only have a limited stroke, or range of displacements. Sometimes the atmospheric turbulence can’t be corrected perfectly.In view of above-mentioned reasons, this paper proposes a new design about deformable mirrors to improve the wavefront correction part in such system. The structure and the advantage of this design will be discussed in the first place. Furthermore, a little change will be made to this design, and the control method will also be discussed. By analyzing the link between the slope information of wavefront and Zernike polynomials, it could be proved that the combination of deformable mirrors affects the reconstruction of wavefront. The introduction of the coherence time explains that such design could make this system perform better. Finally, the relationship between the fitting error, the Strehl ratio and the aperture number of deformable mirrors will be analyzed in a detailed way. This design will be proved to be good for the correction effect by combining with the atmospheric structure constant in Hefei and performing the simulation analysis.The advantage of this design is that the cost is low and the configuration is simple. Further, there is no additional requirement for the manufacturing process of the deformable mirror. And it is easy to increase the stroke further by iterate the procedure to add more deformable mirrors. Therefore, there are some practical values to promote this design.