Key Technology Study Of Liquid Crystal Adaptive Optics System For Two Meters Telescope

Liquid crystal adaptive optics technology is more and more popular based on its advantages of lots of correction cells, large correcting value and low price. In recent years, the liquid crystal adaptive optics system(LCAOS) corresponding with the large aperture telescope got a good observation result, which establishes the foundation for the engineering of liquid crystal adaptive optics technology. With the enlargement of the telescope aperture and the increase of the image resolution, the telescope system enhances the demand to the LCAOS. For example, as the key element, the Shack-Hartmann wavefront sensor(SH-WFS) should be ensured optical structure and precise position in the system. The atmospheric dispersion corrector(ADC) should be added to compensate the effect of atmospheric dispersion on the system image. The optical elements in the system should have good support structure although its aperture is larger. The article studied the key technology of the LCAOS for two meters aperture telescope.The SH-WFS was designed. Aiming at a condition of a 2-meter telescope aperture and the atmospheric coherent length of 10 cm, the lens of SH-WFS was designed and analyzed in simulation. The lens was assembled on the EMCCD. For satisfying the demand of high accuracy and good stability in the LCAOS, we designed a two dimension adjustable mechanism for the SH-WFS based on the slider-crank mechanism. On the pitch and azimuth directions, the adjustment accuracy are ±0.43 arc second and ±2.1 arc second respectively, which satisfied the design demand of 6 arc second.The effect of the atmospheric dispersion on imaging under different zenith angles was analyzed. Convenient to the compact design, we chose the rotation ADC(RADC) consisted of two identical glued wedge-shaped plates. The symmetrical and inverted rotation of the glued plates can generate different atmospheric dispersion compensation for different zenith angle. We chose the materials FK51 and QK3 for the glued plate based on the key wavelength 785 nm of liquid crystal wavefront corrector(LCWC) for maintaining the original image position after the atmospheric dispersion correction. To control the rotation angle of the glued palates automatically, we designed a mechanical structure for the ADC based on the worm and gear mechanism that has the advantages of large transmission ratio and smooth transmission.To detect the rotation angle accuracy of the hollow shafts assembling the glued plates in the ADC, a rotation angle detection device was designed based on the autocollimator. Basing on the refraction of the optical wedge, the rotation angle detection device not only can measure the rotation angle with large range, it also can suppress the detection error induced by the axis wobbly error. Its measurement accuracy comes up to one arc minute. We used this detection system to measure the rotation angle error of the hollow shafts and the results were ±0.05 degree and ±0.07 degree, which all satisfied the design demand of ±0.1 degree.We use the equivalent stress model to analysis the whole bonded mirror, which can improve the efficiency of the simulation for small and middle mirror. Using the equivalent stress to analysis the effect of the temperature on the mirror from the simulation and experiment can prove the feasibility.From the single adjustment for every foundation element to the joints of the elements, an adjustment project was proposed to get the correct position for every optical element. A detecting device was designed to realize the adjustment of the optical parts whose precise can up to 5 arc second. A measure was proposed to achieve the aperture alignment between the liquid crystal corrector and SH-WFS. SH-WFS detects the defocus from the liquid crystal corrector and achieve the accurate aperture alignment A detection method was proposed based on the Zygo interferometer and SH-WFS to accomplish the detection of every foundation elements and LCAOS. The wavefront aberration RMS of detection part and correction part are 0.09λ and 0.06λ, which all satisfied the design demand of 0.1λ λ 632.8nm.This article study the key technology of the LCAOS corresponding with the two meters aperture telescope, which establishes the foundation of the liquid adaptive optics technology and provides the design experience for adaptive optics system corresponding with the large apertures telescopes such as four meters and eight meters.