【摘要】：太赫茲同軸數(shù)字全息技術具有光路簡單、光源相干性要求低、易操作等優(yōu)點,而且系統(tǒng)分辨率只受限于探測裝置的數(shù)值孔徑,因此越來越受到學者們的關注。但由于零級衍射光和共軛像的存在,會造成重建像細節(jié)模糊,影響重建像的質(zhì)量,因此,有關重構算法的研究和討論十分必要。另外,由于太赫茲光源不穩(wěn)定、能量低以及探測裝置靈敏度低等原因,有關太赫茲同軸數(shù)字全息的研究報道多只停留在實現(xiàn)層面,故其分辨率有待進一步研究。本文基于CO2泵浦的連續(xù)太赫茲激光器和熱釋電面陣探測器組成的太赫茲同軸數(shù)字全息成像系統(tǒng),對單次曝光和二次曝光相位恢復算法及其關鍵問題進行了相關的研究,并仿真研究了該實驗條件下,記錄距離和探測器參數(shù)對單點分辨率的影響。為了使相位恢復算法更好地應用于非孤立物體太赫茲同軸數(shù)字全息重建,考慮到已有的相位恢復算法和太赫茲成像特性,提出了一種基于全息圖擴展與切趾運算的改進的單次曝光振幅約束相位恢復算法(T-APRA);分別利用仿真全息圖和實驗數(shù)據(jù)驗證了該單次曝光相位恢復算法在太赫茲同軸數(shù)字全息中具有可行性和適用性;同時,當成像目標為非孤立物體時,針對全息圖擴展、全息圖疊加幀數(shù)對改進的單次曝光振幅約束相位恢復算法重建結果的影響進行了相關的分析;另外,提出了一種基于閾值分割和形態(tài)學濾波的計算物面支持域的方法,并結合改進的單次曝光支持域約束相位恢復算法進行了重建,分別利用仿真全息圖和實驗數(shù)據(jù),對算法的有效性和實用性進行了驗證。在單次曝光相位恢復算法(T-APRA)的基礎上,增加曝光次數(shù),給出了兩次曝光振幅約束相位恢復算法(DT-APRA)的基本計算流程;基于相同的仿真和實驗數(shù)據(jù),對比分析了單次曝光相位恢復算法與兩次曝光相位恢復算法的作用效果;最后,分析了全息圖疊加幀數(shù)對兩次曝光振幅約束相位恢復算法的影響,以便通過減少全息圖記錄幀數(shù)減少獲取全息圖的時間。最后,基于Fournier等人在逆問題框架下提出的單點分辨率計算原理,計算了2.52太赫茲同軸數(shù)字全息成像系統(tǒng)中,物平面在探測器大小范圍內(nèi)單點分辨率的分布圖;研究了不同的記錄距離和探測器參數(shù)對各位置單點分辨率的影響。
[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.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TP391.41;TN26

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本文編號：2138383