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题名	基于电寻址空间光调制器的光束控制关键技术研究
作者	程煜
文献子类	硕士
导师	范薇
关键词	光束控制 beam control 电寻址液晶空间光调制器 electrical-addressed liquid crystal spatial light modulator 附加位相 additional phase 黑栅效应 black gate effect 复振幅调制 complex amplitude modulation
其他题名	Researches on Key Techniques of Beam Control Based on Electrical-addressed Spatial Light Modulator
英文摘要	高功率激光装置系统中，为了提高激光光束的近场填充因子，提高能量利用率，需要对前端系统注入的高斯光束进行空间整形。主动光束整形器件——液晶空间光调制器（liquid crystal spatial light modulator，简称LC-SLM）凭借其高对比度，高分辨率，可编码等优点，已经成为重要的空间整形器件。电寻址液晶空间光调制器已实现高度商品化，振幅型和位相型调制器也被广泛应用于科学研究。本文对电寻址液晶空间光调制器所存在的一些问题进行了分析，并研究了利用纯位相型空间光调制器进行光束复振幅调制的整形方案，理论分析了复振幅调制技术在高功率激光装置中的整形能力。主要内容分为三个部分： （1）从液晶的光学偏振特性出发分析液晶对透过率和附加位相的影响，得出了电寻址液晶光阀的Jones矩阵，并分析了液晶的振幅调制和位相调制模式的差异：从材料上来说，振幅调制模式需要扭曲向列型液晶，而位相调制模式需要向列型液晶；从调制效果来说，液晶光阀可以实现纯位相调制，但无法实现纯振幅调制，在振幅调制时会引入附加位相。通过数值拟合，得到了振幅调制时透过率和附加位相的对应关系，并对附加位相在高功率激光装置中的影响进行了分析。 （2）理论分析并去除电寻址液晶空间光调制器的“黑栅”效应。具体工作如下： I. 基于电寻址液晶光阀的寻址结构，理论分析了“黑栅”效应对光束整形的影响。黑栅会使成像结果变得模糊，降低分辨率，还会产生多级衍射像，降低衍射光的利用率。 II. 提出了小孔滤波去除“黑栅”效应的方案，通过MATLAB仿真计算最大滤波半径rmax和最佳滤波半径rbest。计算发现，当黑栅结构保持不变时，入射光束口径对滤波孔衍射极限倍数选取起重要作用。另外，小孔滤波对空间能量的利用率为83.59%，可保证能量的有效通过。 III. 研究了电寻址液晶光阀的开口率对整形效果的影响，为了达到更高的精度控制能力，使整形误差小于2.25×10?-5，空间光调制器的开口率最好大于64%。 （3）利用纯位相型液晶空间光调制器和空间滤波器实现了光束的复振幅调制，大大降低整形光路的复杂性。具体工作如下： I. 根据高功率激光系统的要求将高斯光束整形成中心反抛物线，边缘超高斯分布的目标光束，并同时将位相整形成目标分布，证明了复振幅调制技术的整形效果。 II. 以平顶超高斯光束为目标光束，分析了高功率激光系统中，滤波小孔大小和位相调制周期对整形结果的影响。得出结论：位相板周期数越小整形精度越高，但出于成本和制作难度考虑，周期数取8或16像素为宜；若系统要求的误差水平为均方根误差小于10%，滤波孔半径的变化范围为20-40倍衍射极限。 III. 理论计算了强度调制中不同截止频率对应的滤波孔选取范围：利用呈中心对称的周期性正弦函数强度分布，研究了高功率激光系统中，不同频率成分的强度调制误差随滤波孔大小的变化情况，并由此分析为了让强度分布中高频成分通过，滤波孔的合理选取范围。 IV. 分析了系统“预屏蔽”能力，研究当系统滤波孔取不同大小时，屏蔽小孔的最小半径。若系统要求的误差水平为均方根误差小于10%，当滤波孔取10DL（10倍衍射极限，diffraction limit，简称DL）时，最小屏蔽孔直径为0.77mm（n=8）；滤波孔取20DL时，最小屏蔽孔直径为0.38mm（n=16）；滤波孔取30DL时，最小屏蔽孔直径为0.25mm（n=25）；滤波孔取40DL时，最小屏蔽孔直径为0.18mm（n=34）。; In the high power laser system, in order to improve the near-field filling factor and the energy utilization rate, it is necessary to carry out the beam shaping of the Gaussian beam injected into the frontend system. Liquid crystal spatial light modulator(LC-SLM) have become a very important subject in space shaping researches because of its advantages, such as high contrast，high resolution, programmable, etc. The electrical-addressed LC-SLM have been highly commercialized, and the amplitude SLM and phase SLM have also been widely used in scientific research. In this paper, some problems of the electrical-addressed SLM are analyzed, and the complex amplitude modulation using a phase-only SLM is studied. The shaping ability of the complex amplitude modulation in the high power laser system is theoretical analyzed. The results are summarized as follows: (1) The influence of the liquid crystal on the transmittance and the additional phase is analyzed based on the optical polarization characteristics of the liquid crystal. The Jones matrix of the electrical-addressed LC-SLM is obtained. The difference between the amplitude modulation mode and phase modulation mode is also analyzed. The amplitude modulation mode requires a twisted nematic liquid crystal, while the phase modulation mode requires a nematic liquid crystal. Meanwhile, the LC-SLM can achieve pure phase modulation, but cannot achieve pure amplitude modulation., as amplitude modulation introduces additional phase. The correspondence between the transmittance and the additional phase in amplitude modulation is obtained by numerical fitting, and the influence of the additional phase in the high power laser device is analyzed. (2) Theoretical analysis and removal of the ‘black gate’ effect of the electrical-addressing LC-SLM is realized. The specific word is as follows: I. Based on the addressing structure of the electrical-addressed LS-SLM, the influence of the ‘black gate’ effect on the beam shaping is analyzed theoretically. ‘Black gate’ will not only reduce the resolution by making the imaging results blurred, but also produce multi-level diffraction image, reducing the utilization of diffracted light. II. Proposed the scheme to remove the ‘black gate’ effect by using a spatial filter. Through MATLAB imitation, the maximum filter radius and the optimum filter radius is calculated. It has been found that the aperture of the incident beam plays an important role in the selection of the diffraction limit multiple of the filter when the ‘black gate’ structure remains unchanged. In addition, the utilization rate of the beam energy in this scheme is up to 83.59%, which guarantees the light can pass the filter effectively. III. The influence of the filling factor of the electrical-addressed LC-SLM on beam shaping is studied. In order to achieve a higher modulation accuracy, so that the shaping error is less than 2.25×10?-5, the SLM’s filling factor should be greater than 64%. (3) Using the phase-only LC-SLM and the spatial filter to realize the complex amplitude modulation, the complexity of the shaping optical path is greatly reduced. I. According to the requirements of high power laser system, the Gaussian light is transformed into the target intensity distribution: anti-parabolic distribution in the center and super-Gaussian distribution on the edge. The phase distribution is transformed into the target distribution as well. The shaping ability of the complex amplitude modulation technology is proved. II. Taking the flat-top super-Gaussian beam as the target intensity distribution, the influence of the size of the filter and phase plate period on the shaping results in the high power laser system is analyzed. The conclusion is that the smaller the phase modulation period, the higher the shaping accuracy. However, considering the cost and production difficult, the number of the phase plant period should be 8 or 16 pixels. If the system requires the root mean square error to be less than 10%, the radius of the filter hole changes in the range of 20-40 times the diffraction limit. III. The calculated range of the filter hole corresponding to the different cutoff frequencies in the intensity modulation is calculated theoretically: the intensity modulation error of different frequency components in the high power laser system is studied by using the centrally symmetric periodic sine intensity distribution. In order to allow the high frequency components of the intensity distribution to pass through, the acceptable range of the filter hole is calculated. IV. Analyzed the system ‘pre-shield’ ability. Calculated the minimum radius of the shield hole when the system filter hole takes different sizes. If the system requires the root mean square error to be less than 10%, we can draw the conclusion. When the filter hole is 10DL, the minimum shielding hole diameter is 0.77mm (n=8); when the filter hole is 20DL, the minimum shielding hole diameter is 0.38mm (n=16); when the filter hole is 30DL, the minimum shielding hole diameter is 0.25mm (n=25); when the filter hole is 40DL, the minimum shielding hole diameter is 0.18mm (n=34).
学科主题	光学工程
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/30928]
专题	中国科学院上海光学精密机械研究所
作者单位	中国科学院上海光学精密机械研究所
推荐引用方式 GB/T 7714	程煜. 基于电寻址空间光调制器的光束控制关键技术研究[D].

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