Thermal stability test and analysis of a 20-actuator bimorph deformable mirror |
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Authors: | Ning Yu Zhou Hong Yu Hao Rao Chang-Hui and Jiang Wen-Han |
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Institution: | College of Photon-electron Science and Engineering, National University of Defense Technology, Changsha 410073, China;Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China;.; Graduate School of the Chinese Academy of Science, Beijing 100039, China |
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Abstract: | One of the important characteristic of adaptive mirrors is the
thermal stability of surface flatness. In this paper, the thermal
stability from 13${^\circ}$C to 25${^\circ}$C of a 20-actuator
bimorph deformable mirror is tested by a Shack--Hartmann wavefront
sensor. Experimental results show that, the surface P--V of bimorph
increases nearly linearly with ambient temperature. The ratio is
0.11\,$\mu$m/${^\circ}$C and the major component of surface
displacement is defocused, compared with which, astigmatism, coma
and spherical aberration contribute very small. Besides, a finite
element model is built up to analyse the influence of thickness,
thermal expansion coefficient and Young's modulus of materials on
thermal stability. Calculated results show that bimorph has the best
thermal stability when the materials have the same thermal expansion
coefficient. And when the thickness ratio of glass to PZT is 3 and
Young's modulus ratio is approximately 0.4, the surface instability
behaviour of the bimorph manifests itself most severely. |
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Keywords: | adaptive optics bimorph
deformable mirror thermal stability |
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