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题名:
夏克-哈特曼波前传感器的若干问题分析
作者: 李华强
学位类别: 博士
答辩日期: 2008-06-10
授予单位: 中国科学院光电技术研究所
授予地点: 光电技术研究所
导师: 饶长辉
关键词: 自适应光学 ; 波前探测 ; 夏克-哈特曼波前传感器 ; 动态范围 ; 质心 ; 焦斑 ; 灵敏度 ; 位移
其他题名: Research on the performance of the Shack-Hartmann wave-front sensor
学位专业: 光学工程
中文摘要: 夏克-哈特曼波前传感器作为一种精密的波前测量器件,已经在自适应光学领域里得到了广泛应用,随着科学技术的发展和实际测量对象的需求,夏克-哈特曼波前传感器的应用范围已经扩展到眼科科学、镜面测量、图像重构等领域。本文从以下几个方面对夏克-哈特曼波前传感器进行了分析、研究,①像素灵敏度的不一致性对焦斑质心测量的影响,②提出了基于光电探测阵列的焦斑灵敏度,③改进型的质心计算方法分析,④外推法增大夏克-哈特曼波前传感器的动态测量范围。 传统的夏克-哈特曼波前传感器大都采用CCD作为光强接收器件,CCD成像质量高但帧频较慢,不能满足目前高测量速度的要求,因此用CMOS传感器代替CCD成为一种趋势。相对于CCD来说,CMOS传感器具有价格便宜、功耗低、帧频快等优点,然而特殊的像素点结构和掺杂工艺,导致每个像素点对光能的转化效率存在差异,外在表现为像素点的灵敏度不一致,这种情况势必会影响焦斑质心的计算精度。本文从离散质心误差传递公式出发得出了像素点灵敏度的不一致性对质心测量的影响,并通过实验对公式进行了验证,实验结果说明了公式的正确性。 夏克-哈特曼波前传感器子孔径上波面的起伏和焦斑的偏移量之间是一个线性关系,光电探测器对焦斑偏移量的探测能力直接反映了波面的测量精度。本文利用焦斑位移灵敏度这样一个概念来描述光电探测器对焦斑偏移量的探测能力,并最终给出焦斑位移灵敏度的函数表达式和数字计算结果。在推导过程中,考虑到了像素点的结构、占空比、焦斑半径以及相机的位分辨率等因素,这为优化设计夏克-哈特曼波前传感器提供了一定的理论依据。 夏克-哈特曼波前传感器的测量精度主要受限于子孔径内焦斑质心的测量精度,Sung-Hoon Baik利用带有权重的像素点输出来计算焦斑质心,本文对这种改进型的焦斑质心算法进行了理论分析,得到了不同权重情况下的离散采样误差、光子噪声误差、读出噪声误差、暗背景噪声误差的表达式,并给出了最终的数值计算结果,最终通过实验的方法给出了某个特定情况下的最优权值。 夏克-哈特曼波前传感器的动态范围定义为仪器能够测量的最大波前起伏,当被测对象超出夏克-哈特曼波前传感器的动态范围时,焦斑将偏离出子孔径在探测器上的对应区域,也就是说焦斑和子孔径之间的对应关系不再明显,因此需要一种方法重新找出二者之间的对应关系。本文首先对影响夏克-哈特曼波前传感器动态范围的各种因素进行了深入分析,并在前人研究的基础上,提出了一种新型的软件处理方法-外推法来增大夏克-哈特曼波前传感器的动态测量范围,在已知某个或某些子孔径、焦斑对应关系的情况下,可以利用外推法得到与此子孔径相邻的所有子孔径对应的焦斑。相对于以往的方法,外推法具有无需改动硬件、处理速度快、编程灵活等优点。
英文摘要: Shack-Hartmann Wave-front Sensor has been a popular wave-front sensing instrument in various areas such as optical testing, astronomical adaptive optics and ophthalmology since its invention. This dissertation concentrates on resolving the following problems which come from the practice application, such as the centroid error of far-field influenced by the non-uniformity of pixels, the displacement sensitivity of far-field spot detected by opt-electronic array and the analysis of the modified centroid algorithm, extending the dynamic range of Shack-Hartmann wave-front sensor. CMOS (Complementary Metal-Oxide-Semiconductor Transistor) camera, which has high frame rate, can be used in the Shack-Hartmann Wave-front Sensor to obtain the spot image. Each pixel of CMOS camera has own amplifier, which leads to the non-uniformity of sensitivity. So the centroid error caused by the non-uniformity of sensitivity must be considered. In this paper, the theoretical expression of centroid error induced by the non-uniformity sensitivity of pixels is given and demonstrated through experiment. The results show for a special detector, the error has no relationship with the spot size, incident energy, and other factors. To the CMOS camera mentioned in this paper, the error is less than 0.015pixels. Digital optoelectronic array is conventionally used to detect the far-field spot, and the output of the detector could be changed for the displacement of far-field spot. In this paper, displacement sensitivity of the far-field spot, which is defined as the minimum displacement that can cause the output of digital photoelectric array changed an output unit, is analyzed theoretically. The numerical computation results are presented. The results show that the displacement sensitivity is the function as the spot size, the optical fill factor, data resolution and sensitivity of the digital optoelectronic array. The digital optoelectronic array has the highest displacement sensitivity while the spot size is about 1 pixel. The effect of the optical fill factor on displacement sensitivity is decreasing while the spot size increases grandly. The accuracy of the Shack-Hartmann wave-front sensor for measuring a wave-front distortion is mainly dependent upon the measuring accuracy of the centroid of each spot. Compared with CCD, CMOS camera has fixed pattern noise, sensitivity non-uniformity besides the readout noise. In this paper, flat-field method is used to eliminate the fixed pattern noise and rectify the sensitivity non-uniformity. A modified centroid algorithm, which uses some power from the gray level intensity of the spot images instead of the gay level intensity itself, is introduced in theory and applied to calculate the centroid. The results show that the modified centroid algorithm and flat-field method are both powerful tool to improve the detection accuracy and repeatability, and the optimum power of the modified centroid algorithm result from the tradeoff between the centroid error caused by the sampling error and other noise. The dynamic range of the Shack-Hartmann Wave-front Sensor means the maximum tolerable aberration of the incident wave-front. In a conventional Shack-Hartmann Wave-front Sensor, the spots are required to lie inside a sub-aperture defined by the original lenslet. If a wave-front varies so fast that the spot's displacement goes beyond the sub-aperture, the spots cannot be assigned to the original lenslet and the reference focal spot. The spot displacements cannot be determined without knowing the reference position. A novel method- extrapolation method is introduced to assign the correct reference positions to the focal spots even if they leave their original sub-aperture. If the focal spot of sub-aperture (A) is known, then the focal spots of sub-apertures around A can be assigned by the extrapolation method. Compared with the other prior methods, extrapolation method has two advantages: one is little time cost; the other the extrapolation method is a software method and easy to be achieved through flexible programs.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ioe.ac.cn/handle/181551/279
Appears in Collections:光电技术研究所博硕士论文_学位论文

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Recommended Citation:
李华强. 夏克-哈特曼波前传感器的若干问题分析[D]. 光电技术研究所. 中国科学院光电技术研究所. 2008.
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