20单元双压电片变形镜的性能测试与闭环校正实验研究

Performance test and closed-loop correction experiment of a 20-element bimorph deformable mirror

测试了20单元双压电片变形镜的影响函数、变形量-电压特性曲线、面形热稳定性和频率响应特性,并搭建基于20单元双压电片变形镜和13×13阵列哈特曼传感器的自适应光学系统,测试了该变形镜对自身初始面形和静态像差板的闭环校正效果.实验结果表明,各分立电极变形量对加载电压的平均灵敏度为0.57μm/100 V,离焦电极的灵敏度为1.09μm/100 V;各电极变形量-电压响应曲线均存在迟滞现象,滞后量在最大变形量的10%以内;在温度引起的双压电片变形镜面形变化中离焦项贡献最大,其变化对温度也最为敏感,在13℃到25℃的测试区间内,离焦项P-V值增大了1.37μm,而像散、彗差和球差项的P-V变化均小于0.15μm;该变形镜对于频率在0—3 kHz范围内的电压输入信号可以均匀、稳定的响应,谐振频率在4 kHz左右.闭环条件下,双压电片变形镜能够对自身面形和静态像差板进行有效校正,校正前后焦平面上的远场光斑质量得到显著提高,Strehl Ratio分别从0.02和0.03提高到0.95和0.54.

Performances of a 20-element bimorph deformable mirror are measured and a closed-loop adaptive optics system, which consists of the bimorph mirror and a Shack-Hartmann wave-front sensor with 13 × 13 sub-aperture array, is established to test the mirror＇s capability of correcting static aberrations. Experimental results show that, the mean displacement response to voltage of discrete actuators is 0.57μm/100 V and that of defocus electrode is 1.09 μm/100 V. The hysteresis of actuator is limited to ten percents of the maximal displacement. With the ambient temperature increasing from 13 ℃ to 25 ℃, the P-V of defocus of the mirror surface is enlarged by 1.37 μm and the P-V of other distortions, such as astigmatism, coma and spherical aberration, is enlarged by 0. 15 μm. The frequency response of the bimorph mirror is about 4 kHz. When the closed-loop control is on, intensity distributions at the image plane of distorted wave-fronts are effectively improved. The Strehl ratios increase from 0.02 to 0.95, and 0.03 to 0.54, respectively.