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题名	基于轴对称走离效应选模机理的径向偏振光纤激光器研究
作者	孙雪焕
文献子类	硕士
导师	李建郎
关键词	径向偏振 Radial Polarization 掺镱光纤激光器 Ytterbium-doped Fiber Laser 轴对称走离效应 Axis-symmetrical Walk-off Effect 被动调Q Passive Q-switch
其他题名	Radially Polarized Yb-doped Fiber Laser Using Axis-symmetrical Walk-off Effect for Mode Discrimination
英文摘要	近年来，随着人们对光的偏振特性研究的不断深入，具有空间轴对称分布的圆柱矢量偏振光越来越吸引科研人员的关注。其中，最具代表的圆柱矢量偏振光主要包括径向偏振光和切向偏振光，在经过高数值孔径透镜聚焦时，在焦点处会产生一个很强的纵向电场或磁场分布。基于这些特性，圆柱矢量偏振光被广泛应用于粒子捕获、电子加速、材料加工、表面等离子体激发以及近场扫描光学探针等众多领域。特别地，在金属加工时，为了降低材料的熔覆阈值和提高加工精度，急切需求高峰值功率和短脉冲宽度的圆柱矢量偏振激光。 众所周知，相比于固体激光器，稀土离子掺杂的光纤激光器具有增益高、散热效果好、模式约束力强等优点，吸引了科研人员越来越浓的兴趣。迄今为止，连续波运转的径向偏振光纤激光器已经被大量研究与报道。同时，相比于连续光输出的激光器，调Q技术可以获得高峰值功率、窄脉冲宽度的脉冲激光输出，使得如何获得调Q运转的径向偏振光纤激光器成为研究热点。 在本论文的研究中，基于轴对称走离效应选模机理。第一步，我们首先实现了高功率、高效率连续输出的径向偏振掺镱光纤激光器。在进一步的实验中，通过分别采用Cr4+:YAG晶体和半导体可饱和吸收镜（SESAM）作为可饱和吸收体，获得了被动调Q的径向偏振掺镱光纤激光器。实验证明，基于单轴晶体走离效应的径向偏振光纤激光器具有结构紧凑，成本低，易于实现大规模生产应用的优势。 本论文的主要内容如下： 第一章，本章对圆柱矢量偏振光的基本概念进行了概述，包括圆柱矢量偏振光与传统偏振光的区别、圆柱矢量偏振光在光纤中传输时的偏振态演化过程以及圆柱矢量偏振光的紧聚焦特性、数学描述、应用前景和产生方法。 第二章，基于轴对称走离效应选模机理，开展了连续输出的、径向偏振的掺镱光纤激光器实验研究。实验中，采用掺镱双包层光纤作为增益介质，选用长度为20 mm的c切YVO4单轴晶体作为腔内选模元件，利用双折射晶体的走离效应，成功获得了斜坡效率高达68.4%，最大输出功率4.06 W的径向偏振激光输出。 第三章，基于轴对称走离效应选模机理，开展了基于Cr4+:YAG被动调Q、径向偏振的掺镱光纤激光器实验研究。实验中，基于c切YVO4单轴晶体的轴对称走离效应作为选模机理，实现了径向偏振的被动调Q脉冲输出。输出激光斜坡效率高达66.5%，最大平均输出功率为3.89 W。在最大吸收泵浦功率为 6.48 W 时，激光脉冲的脉宽为 160 ns，重复频率为 151 kHz，峰值功率为161 W。 第四章，基于轴对称走离效应选模机理，开展了基于SESAM被动调Q、径向偏振的掺镱光纤激光器实验研究。首先介绍了SESAM用于被动调Q和锁模的背景知识。实验中，基于c切YVO4单轴晶体的轴对称走离效应作为选模机理，采用SESAM作为可饱和吸收体，在光纤激光器中实现了径向偏振的被动调Q脉冲输出。该激光器的斜坡效率为28.2%，在吸收泵浦功率3.72 W 时，平均输出功率为0.895 W，脉冲重复频率为75 kHz。 第五章，对本论文的主要研究工作和研究成果进行了总结，并结合实验中遇到的问题对未来工作进行展望。; In recent years, cylindrical vector beams (CVBs), having axis-symmetrical intensity distribution and on-axis polarization singularity and typically including radially and azimuthally polarized beams, have attracted increasing attentions. CVBs can be tightly focused when applying high-numerical-aperture lens and also form strong longitudinal electric or magnetic field at the focal spot. Owing to these unique features, CVBs have been applied widely in many fields, such as particle trapping, electron acceleration, material processing, excitation of surface plasma, near field scanning optical microscope probe, etc. Furthermore, for the specific applications like metal cutting, CVBs with high peak power and short duration are desired for reaching the ablation threshold and improving the precision. In other hands, compared with the solid-state lasers, the rare-earth doped fiber lasers are advantageous for high gain, excellent thermal dissipation and good modal confinement. Up to date, lots of endeavors have been devoted to continuous-wave, radially polarized fiber laser. Furthermore, as Q switching allows the production of a high-peak-power pulse, the Q-switched and radially polarized fiber laser also becomes vital for the generation of energetic pulse with vector polarization. In the study of this thesis, we utilized the axis-symmetrical walk-off effect as the intra-cavity mode discrimination. In the first step, we demonstrated a continuous-wave and radially polarized ytterbium-doped fiber laser with high power and high efficiency. In the second step, we realized Q-switched, radially polarized ytterbium-doped fiber laser by using Cr4+:YAG and semiconductor saturable absorber mirror (SESAM) as the saturable absorbers, respectively. These results verified that our radially polarized fiber laser was simple, compact, low-cost and easy to mass production. The main contents of the thesis are given as follows: In chapter one, the basic knowledge on CVBs was overviewed, including polarization state, focusing, mathematical description, the applications and the methods for their generation. In chapter two, we used axis-symmetrical walk-off effect of a uniaxial crystal for mode discrimination, and demonstrated an ytterbium-doped fiber laser that emitted radially polarized light with high power and high efficiency. In the experiment, we used an ytterbium-doped double-cladding fiber as the gain medium, and used a 20-mm length c-cut YVO4 crystal for the intracavity mode discrimination, and successfully obtained a radially polarized laser output with high efficiency of 68.4% and maximum output power of 4.06W. In chapter three, we used axis-symmetrical walk-off effect of a uniaxial crystal for mode discrimination, and demonstrated a radially polarized ytterbium-doped fiber laser passively Q-switched by a Cr4+:YAG crystal saturable absorber. In the experiment, using c-cut YVO4 crystal’s walk-off effect for intracavity mode discrimination, a passively Q-switched, radially polarized Yb-doped fiber laser pulse was obtained. The maximum averaged laser power reached 3.89 W with a high slope efficiency of 66.5%. The laser pulse had a peak power of 161 W, 160 ns duration and 151 kHz repetition rate at the absorbed pump power of 6.48 W. Such a radially polarized pulse would facilitate numerous applications. In chapter four, we used axis-symmetrical walk-off effect of a uniaxial crystal for mode discrimination, and demonstrated a radially polarized ytterbium-doped fiber laser passively Q-switched by a SESAM saturable absorber. Firstly, we introduced the background on the SESAM for Q-switching and mode-locking. In the experiment, using c-cut YVO4 crystal’s walk-off effect for intracavity mode discrimination and SESAM as saturable absorber, we obtained a passively Q-switched, radially polarized Yb-doped fiber laser pulse with slop efficiency of 28.2% and average power of 0.895 W, and the laser pulse have 75 kHz repetition rate at the absorbed pump power of 3.72 W. In chapter five, the results of this thesis were summarized, and the prospect of our fiber laser was discussed.
学科主题	光学工程
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/31033]
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	孙雪焕. 基于轴对称走离效应选模机理的径向偏振光纤激光器研究[D].

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