基于衍射光学元件的相干激光阵列合束技术研究
文献类型：学位论文
| 作者 | 李兵 |
| 学位类别 | 博士 |
| 答辩日期 | 2013 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 刘立人 |
| 关键词 | 相干合束 衍射光学元件 光栅优化设计 误差分析 相位检测 |
| 其他题名 | Research on Diffractive-Optical-Element based Coherent Laser Array Combining Technologies |
| 中文摘要 | 随着高能激光在医学、激光核聚变、高能激光武器等领域的应用越来越多，并且这些应用对激光束的质量要求越来越高，如何得到高功率、高质量的激光束成为一项重要的研究课题。然而，单一激光器由于自身的缺陷，如增益饱和、热效应、非线性效应等，其输出功率的提高受到了限制。通过对激光阵列输出光束进行相干合束来获得高功率、高质量的激光束是一种非常有效的方法。衍射光学元件，尤其是二元光学元件，具有结构简单、体积小、衍射效率高、成本低及易于大面积加工的优点。作为二元光学元件中的一种位相型光栅，达曼光栅在入射光照射下可以产生一定数目的等光强光斑阵列。由傅里叶变换理论，逆用达曼光栅的分束作用，将相干激光阵列视为等光强光斑阵列，经傅里叶透镜变换后，经共轭逆达曼光栅对合束光场进行相位调制，消除了合束光场相位分布的不均匀性，即可实现激光阵列相干合束，得到远场单一主瓣的高亮度光束。 本文主要从以下几个方面对基于衍射光学元件（达曼光栅）的相干激光阵列合束技术进行了研究： 1. 共轭逆达曼光栅用于光纤激光阵列相干合束理论分析和模拟实验研究。分析了衍射光学元件用于激光阵列相干合束的物理模型和数学模型，利用Matlab进行了合束过程的数值模拟以及光栅加工和放置误差对合束效率的影响的数值分析；数值模拟了共轭逆达曼光栅用于5×5光纤激光阵列相干合束的模拟实验方案，测量了合束效率及光栅放置误差对于合束效率的影响；最后分析了采用连续光栅来提高系统合束效率的可行性。 2. 达曼光栅的优化设计。通过增加突变点等手段，尝试提高达曼光栅的效率；提出了可以产生等光强但仅有三个位相值的子光束阵列的达曼光栅概念；采用遗传算法对各子光束光强和位相同时进行优化，得到了两组1×5和一组1×4高衍射效率的三相位达曼光栅；加工了4×4和5×5达曼光栅，并进行了基本测量。 3. 基于共轭逆达曼光栅的大尺寸固体激光阵列相干合束理论分析和模拟实验研究。将共轭逆达曼光栅用于大尺寸固体激光阵列的相干合束中，采用可增加21.5%阵列占空比的方形孔径，进行了相应的理论模拟和数值误差分析；从数学上证明了系统的合束效率等于光栅的分束效率，与激光器口径、光强分布无关；进行了相应的4×4偶数阵列和5×5奇数阵列的合束模拟验证实验，得到了90%最高效率下的误差边界值，理论分析与实验结果相符。 4. 达曼光栅分束子光束阵列位相测量。首次提出对光栅分束子光束进行位相测量的问题；设计了基于电光晶体四步移相的Mach-Zehner式的实验方案；利用Matlab分析了傅里叶透镜焦点位置精度对各衍射子光束位相的影响，以便提高位相测量精度；进行的4×4两相位达曼光栅位相测量实验，并与理论结果进行了对比。 本文讨论了达曼光栅用于相干激光阵列合束的基本原理，建立了完整的数学模型，优化设计了达曼光栅，进行了共轭逆达曼光栅用于光纤和固体激光相干阵列的理论分析和模拟验证实验研究，同时测量了等位相等光强分束达曼光栅子光束阵列位相。由于所用的达曼光栅存在效率较低的问题，限制的整个系统的合束效率，因此需要进一步的优化设计高效率的光栅；同时，作为描述高功率激光系统的参数的光束质量，本文并未涉及，下一步工作需分析加工、装配等误差对于光束质量的影响。 |
| 英文摘要 | With the applications of high power lasers in physics, laser nuclear fusion, high power laser weapons etc. and these applications require high laser beam quality, how to get high power, high beam quality laser beam becomes an important issue. However, due to limitations such as gain saturation, thermal effects and nonlinear effects, the output power of one single laser is limited. It’s quite an efficient way to obtain high power, high beam quality coherently combining laser arrays. Diffractive optical elements(DOE), especially binary optical elements, have simple structures, small volume, high diffraction efficiencies, lower costs and are easy to fabricate. As one typical type of phase-grating DOE, Dammann gratings produce equal intensity arrays when illuminated by input lights. According to the Fourier Calculation theorem, the coherent laser array, which can be seen as equal intensity spot array, can be combined by the Fourier lens. By putting an conjugate inverse Dammann grating at the back focal plane, the phase fluctuations of the combined beam can be eliminated and high power, high beam quality laser can be obtained in the far field. In this paper, we mainly discuss this technology in the following aspects: 1. Research of Conjugate Dammann grating based coherent fiber laser array combination. Analyzed the physical and mathematical models of diffractive-optical-element based coherent beam combination, carried out the combining simulations and error analysis with Matlab; Performed the simulated experiment, measured the beam combining efficiency and the influence of the grating position to the combining efficiency; analyzed the feasibility of continuous gratings to be used to improve the beam combining efficiency of the system. 2. Design and optimization of Dammann grating. Tried to improve the diffraction efficiency of the gratings by adding phase transition points; Proposed an improved type of Dammann grating that can produce sub-beam array with equal intensities but only three phases; Obtained one 1×4and two 1×5 gratings with high efficiency with the Genetic Algorithm; fabricated and measured one 4×4 grating and one 5×5 grating. 3. Simulations of Conjugate Dammann grating based 2D coherent solid-state laser array combination. Applied this technique to the combination of large-scale solid-state laser array, adopted the square aperture to increase the fill factor, carried out the numerical simulations and error analysis; Performed the simulation experiments with the fabricated 4×4 and 5×5gratings, obtained the error margins efficiency. 4. Sub-beam phase measurement of Dammann grating. The first to propose the question of sub-beam phase measurement of gratings; Proposed a four-step-phase-shifting Mach-Zehner scheme; Analyzed the influence of the positioning error to the precision of the measured phase values; Performed the sub-beam phase measurement of the 4×4 two-phase grating and compared the experimental results with the theoretical results. Physical and mathematical models of Dammann grating based coherent laser array combining technique are presents. Dammann gratings are optimized. Simulated applications of this technique in the combinations of fiber laser array and solid laser arrays are carried out. The sub beam phases of the equal phase equal intensity Dammann gratings are detected. Since the diffraction efficiency of the Dammann grating is relatively low and the efficiency of the whole system is limited, the future work will be the design of high efficiency gratings. Also, the beam quality of the combined should be studied. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15744]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 李兵. 基于衍射光学元件的相干激光阵列合束技术研究[D]. 中国科学院上海光学精密机械研究所. 2013. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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