| One of the liquid crystal wavefront correctors’(LCWFC) merits is its largenumber of pixels, which makes it possible to be used in visible light. However,because of the dispersion of liquid crystal material, the imaging bandwidth of theliquid crystal adaptive optics system is presently in the range of0.7~0.9um in the Iband. Meanwhile the response speed of the infrared liquid crystal material is slow.There is no commercial liquid crystal wavefront correctors which have been used in aliquid crystal adaptive optics system (LCAOS) in infrared range. On the other hand,because of the limited deformable mirror’(DM) actuators number, the spatial fittingfrequency of DM is low and it is difficult to be used in visible and near-infrared light.Therefore, combined with them together because of their advantages, a new AOSbased on LCWFC and DM is built for realizing high resolution imaging both in thevisible and the infrared wavelengths simultaneously. In the new AO system, we useboth LCWFC and DM as wavefront correctors for different wave lengths. Therefore,the paper finished the following works to investigate the electr-optics characteristicsof WFCs and control method of the new wide bandwidth AOS:Firstly, the response characteristics of the DM and its control method wereinvestigated in detail. Although many references have been reported about the DM inhome and abroad, it’s the first time for us to use it in our AO system. So, it’snecessary to investigate its response characteristics and present an effective controlmethod. And the matching relation between the Shack-Hartmann wavefront sensor and the deformable mirror was designed and measured, and the control method of thedeformable mirror was presented and tested systematically. Based on the results, thestatic aberration is corrected using the DM. The cross-coupling, the modulation of thedriving actuator, the response time and the fitting ability to the zernike surface weretested. The measured response time of DM is2.27ms, and its cross-coupling value isabout40%, its maximum phase modulation is about2um. The first ten zernike modeswith normalized coefficient can be well fitted. Based on that, the pure I controller wasdesigned. The static aberration is6.55(PV) before correction and1.25(PV) aftercorrection.Next, the driving method of the liquid crystal wavefront corrector is studied. TheLCWFC’s response time and quantitative levels under over-driving method wereinvestigated systematically, and their optimized value were obtained. Then based onthe over-driving method, we measured the over-driving matrix of a256×256pixelsLCWFC produced by the BNS company using the polarized light interference method.For the optimal quantitative level of32, the delay time was reduced from2.83ms to1.796ms using the over-driving method. And the open-loop liquid crystal adaptiveoptics system (LCAOS) was composed of LCWFC and the Shack-Hartmannwavefront sensor (SH-WFS). The response matrix of it was measured and the the Icontroller was designed. Using this system, the static aberration was correctedperfectly. The high and low Zernike order correction adaptive-optics system wasdesigned based on LC WFC and DM.DM and SH-WFS is in a closed-loop controlsystem while LCWFC and SH-WFS in an open-loop structure. Theaberration-decoupling method of LCWFC and DM high and low zernike order AOsystem was studied. The response matrix of the AO system was measured by themethod of sending zernike mode one by one, which realizes the aberration decouplingand the control of LCWFC and the DM simultaneously. Finally, the control timesequence of the system was investigated for real-time correction, which settled thefoundation for the further dynamic correction experiments. |
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