基于体布拉格光栅的宽带角选择空间滤波研究

发布时间：2018-04-22 09:06

本文选题：体布拉格光栅 + 角选择滤波　；参考：《苏州大学》2016年博士论文

【摘要】：激光光束控制是高功率激光研究的关键技术之一。在高功率激光装置中,灰尘、镜面上的加工瑕疵以及光学材料自身的不均匀都会在光束中引入振幅或相位调制,降低光束质量。空间滤波器是提高光束质量、实现光束控制的主要方法之一。传统针孔空间滤波器由于其聚焦原理会衍生出其他一些问题,包括等离子体堵孔效应、空气击穿等,因此要求针孔滤波器具有庞大的体积和较高的环境真空度等。记录在光热敏折射率玻璃中的体布拉格光栅由于其具有较高的衍射效率和优秀的布拉格选择特性而被广泛应用在近场角选择空间滤波领域。角选择空间滤波能够在非聚焦的光束近场实现高质量的空间滤波,提高光束强度分布的均匀性。角选择空间滤波器在实际激光装置中应用存在两个问题：一是角选择空间滤波器会使光束发生偏转,难以实现即插即用；二是受体布拉格光栅光谱选择性的制约,角选择空间滤波器难以实现对大带宽(数十纳米)光束的滤波。针对上述问题,本论文提出一种可实现即插即用的宽带角选择滤波方案,能够对带宽高至数十纳米的光束实现高质量的空间滤波,为宽带激光的光束近场质量控制提供了一个新的思路。本论文取得的主要研究结果如下：(1)分析了体布拉格光栅的衍射特性。研究了体布拉格光栅的角响应带宽与光谱响应带宽的关系,二者共同影响体布拉格光栅的衍射效率；提出同时增大体布拉格光栅的厚度和周期,可以在保证角响应带宽不变时获得更大的光谱响应带宽；分析了基于体布拉格光栅的角选择滤波适用范围,并指出对于一定范围内的任意波长都存在一个入射角度使得体布拉格栅的衍射效率最大。(2)首次提出了一种基于体布拉格光栅的宽带角选择空间滤波技术。利用面光栅的色散能力与体布拉格光栅的角度选择能力,在保证角响应带宽的同时将光谱响应带宽提高至数十纳米；基于矢量分析给出了光栅组合的匹配条件。研究结果表明,在可见光至近红外波段,各个波长成分均可被光栅组合高效衍射,实现良好的宽带角选择空间滤波。(3)研究了宽带光束经宽带角选择空间滤波器的衍射特性。采用傅里叶方法与耦合波理论,分析了宽带角选择空间滤波器对有限口径宽带光束的空间滤波效果。模拟结果表明,宽带角选择空间滤波器能够将光束中的中高频调制滤除,且理论设计时只需要考虑体布拉格光栅的角响应带宽。分析了面-体光栅失配对宽带角选择空间滤波器的输出特性的影响。研究结果对于宽带角选择空间滤波器的实际应用具有重要参考价值。(4)开展了宽带角选择空间滤波器的原理验证实验研究。结果表明：光栅组合的输出光束光谱带宽可达到65 nm,当面-体光栅周期失配量较小时可以通过旋转体布拉格光栅补偿输出光束带宽；在空域和频域分析了宽带角选择空间滤波器的滤波能力,目标光束中1mm-1以上的特征空间频率被完全滤除,提高了目标光束近场分布特性。本论文所取得的成果为宽带角选择空间滤波技术奠定了基础,为拓展体布拉格光栅在高功率激光领域的应用提供了一定的参考。
[Abstract]:Laser beam control is one of the key technologies in high power laser research. In high power laser devices, the dust, the defects on the mirror surface and the inhomogeneous of the optical material will introduce the amplitude or phase modulation in the beam to reduce the beam quality. The spatial filter is the main method to improve the beam quality and realize the beam control. Firstly, the traditional pinhole space filter will derive other problems due to its focusing principle, including the plasma plugging effect, air breakdown and so on. Therefore, the pinhole filter is required to have a large volume and a higher environmental vacuum. The volume Prague grating in the light thermal refractive index glass is recorded because of its high diffraction efficiency. The rate and excellent selection characteristics of Prague are widely used in the field of near field angular selection space filtering. Angular selection spatial filtering can achieve high quality spatial filtering in the near field of non focused beam, and improve the uniformity of the intensity distribution of the beam. There are two problems in the application of angular selection space filter in the actual laser device: one is the angle. The selection of spatial filters will make the beam deflect, and it is difficult to achieve plug and play. Two is the restriction of the spectral selectivity of the receptor Prague grating. The angular selection space filter is difficult to realize the filtering of large bandwidth (tens of nanometers). High quality spatial filtering for beams with high bandwidth to dozens of nanometers provides a new idea for the near field quality control of wide-band laser beams. The main results obtained in this paper are as follows: (1) the diffraction characteristics of the body Prague grating are analyzed. The angular response bandwidth and spectral response bandwidth of the body Prague grating are studied. The relationship between the two factors affects the diffraction efficiency of the body Prague grating. The thickness and period of the volume of the body Prague grating can be increased at the same time. The larger spectral response bandwidth can be obtained when the angular response bandwidth is kept constant, and the application range of the angular selection filter based on the body of the body Prague grating is analyzed, and the arbitrary range is pointed out. The diffraction efficiency of the appropriate Prague gate is the largest in wavelength. (2) a broadband angle selection spatial filtering technique based on body Prague grating is proposed for the first time. Using the dispersion ability of the surface grating and the angle selection of the body of the body of the Prague grating, the spectral response bandwidth is increased to the bandwidth of the angular response while increasing the spectral response bandwidth. The matching conditions of the grating combination are given based on the vector analysis. The results show that, in the visible to near infrared wavelengths, all the wavelengths can be diffracted by the grating combination efficiently to achieve a good wideband angular selection spatial filtering. (3) the diffraction characteristics of the wideband beam through the wide band angle selection space filter are studied. The spatial filtering effect of the wide-band angular selection space filter to the limited aperture wideband beam is analyzed with the coupled wave theory and the coupled wave theory. The simulation results show that the wide-band angle selection spatial filter can filter the medium and high frequency modulation in the beam, and the theoretical design only needs to consider the angular response bandwidth of the body Prague grating. The effect of grating mismatch on the output characteristics of wide-band angular selection spatial filter. The results are of important reference value for the practical application of wide-band angular selection space filters. (4) the experimental research on the principle verification of wide-band angle selection spatial filter is carried out. The results show that the spectral bandwidth of the output beam of the grating combination can reach 65 nm, The bandwidth of the output beam can be compensated by the rotating body Prague grating. The filtering capability of the wideband angle selection spatial filter is analyzed in the airspace and frequency domain. The characteristic spatial frequency above the 1mm-1 in the target beam is completely filtered out and the near-field distribution characteristics of the target beam are improved. The results laid the foundation for the wideband angle selective spatial filtering technology, and provided a reference for expanding the application of the volume Prague grating in the high-power laser field.

【学位授予单位】：苏州大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN24

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