连续太赫兹同轴数字全息相位恢复算法和分辨率研究

发布时间：2018-07-22 19:49

【摘要】：太赫兹同轴数字全息技术具有光路简单、光源相干性要求低、易操作等优点,而且系统分辨率只受限于探测装置的数值孔径,因此越来越受到学者们的关注。但由于零级衍射光和共轭像的存在,会造成重建像细节模糊,影响重建像的质量,因此,有关重构算法的研究和讨论十分必要。另外,由于太赫兹光源不稳定、能量低以及探测装置灵敏度低等原因,有关太赫兹同轴数字全息的研究报道多只停留在实现层面,故其分辨率有待进一步研究。本文基于CO2泵浦的连续太赫兹激光器和热释电面阵探测器组成的太赫兹同轴数字全息成像系统,对单次曝光和二次曝光相位恢复算法及其关键问题进行了相关的研究,并仿真研究了该实验条件下,记录距离和探测器参数对单点分辨率的影响。为了使相位恢复算法更好地应用于非孤立物体太赫兹同轴数字全息重建,考虑到已有的相位恢复算法和太赫兹成像特性,提出了一种基于全息图扩展与切趾运算的改进的单次曝光振幅约束相位恢复算法(T-APRA);分别利用仿真全息图和实验数据验证了该单次曝光相位恢复算法在太赫兹同轴数字全息中具有可行性和适用性;同时,当成像目标为非孤立物体时,针对全息图扩展、全息图叠加帧数对改进的单次曝光振幅约束相位恢复算法重建结果的影响进行了相关的分析;另外,提出了一种基于阈值分割和形态学滤波的计算物面支持域的方法,并结合改进的单次曝光支持域约束相位恢复算法进行了重建,分别利用仿真全息图和实验数据,对算法的有效性和实用性进行了验证。在单次曝光相位恢复算法(T-APRA)的基础上,增加曝光次数,给出了两次曝光振幅约束相位恢复算法(DT-APRA)的基本计算流程;基于相同的仿真和实验数据,对比分析了单次曝光相位恢复算法与两次曝光相位恢复算法的作用效果;最后,分析了全息图叠加帧数对两次曝光振幅约束相位恢复算法的影响,以便通过减少全息图记录帧数减少获取全息图的时间。最后,基于Fournier等人在逆问题框架下提出的单点分辨率计算原理,计算了2.52太赫兹同轴数字全息成像系统中,物平面在探测器大小范围内单点分辨率的分布图;研究了不同的记录距离和探测器参数对各位置单点分辨率的影响。
[Abstract]:Terahertz coaxial digital holography has the advantages of simple optical path, low coherence of light source, easy operation and so on. The resolution of the system is limited by the numerical aperture of the detector, so more and more scholars pay attention to it. But because of the existence of zero-order diffraction and conjugate image, the details of the reconstructed image will be blurred and the quality of the reconstructed image will be affected. Therefore, it is necessary to study and discuss the reconstruction algorithm. In addition, because the terahertz light source is unstable, the energy is low and the sensitivity of the detector is low, the research reports of THz coaxial digital holography are mostly focused on the realization level, so its resolution needs further study. Based on the CO2 pumped CW terahertz laser and the terahertz digital holographic imaging system composed of pyroelectric array detector, the phase recovery algorithm and its key problems of single exposure and secondary exposure are studied in this paper. The effects of recording distance and detector parameters on the single point resolution are simulated. In order to better apply the phase recovery algorithm to the terahertz digital holographic reconstruction of non-isolated objects, the existing phase recovery algorithms and terahertz imaging characteristics are considered. An improved single-exposure amplitude-constrained phase recovery algorithm (T-APRA) based on hologram expansion and apodization operation is proposed, and the simulation hologram and experimental data are used to verify the proposed single-exposure phase recovery algorithm in terahertz coaxial. It is feasible and applicable in digital holography. At the same time, when the image object is considered as a non-isolated object, the influence of the number of frames superimposed by the hologram on the reconstruction result of the improved single-exposure amplitude-constrained phase recovery algorithm is analyzed. A method of computing object surface support domain based on threshold segmentation and morphological filtering is proposed. The improved single-exposure support domain constrained phase recovery algorithm is used to reconstruct the object surface. The simulation hologram and experimental data are used respectively. The validity and practicability of the algorithm are verified. Based on the single-exposure phase recovery algorithm (T-APRA), the basic calculation flow of the two-exposure amplitude constrained phase recovery algorithm (DT-APRA) is presented, based on the same simulation and experimental data. The effects of single exposure phase recovery algorithm and double exposure phase recovery algorithm are compared and analyzed. Finally, the effect of the number of superimposed frames of hologram on the amplitude constrained phase recovery algorithm of two exposures is analyzed. In order to reduce the time to acquire the hologram by reducing the number of frames recorded in the hologram. Finally, based on the principle of single-point resolution proposed by Fournier et al in the inverse framework, the distribution of the object plane in the detector range is calculated in 2.52 terahertz digital holographic imaging system. The effects of different recording distance and detector parameters on the single point resolution of each position are studied.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TP391.41;TN26

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