基于内腔双折射选模机理的高效、高功率矢量偏振掺镱光纤激光器研究
文献类型：学位论文
| 作者 | 邹琳 |
| 学位类别 | 硕士 |
| 答辩日期 | 2015 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 李建郎 |
| 关键词 | 矢量光束 掺镱光纤激光器 单轴晶体 被动调Q |
| 其他题名 | Efficient, High-power and Vector Fiber Laser Based on Intracavity Birefringent Mode Discrimination |
| 中文摘要 | 径向偏振和切向偏振光束都是属于圆柱矢量偏振光束，它们具有空间圆对称偏振特性以及环形强度分布特性。这些特殊的性质使得圆柱矢量偏振光束在许多方面优于线偏振光束和圆偏振光束。例如，这类光束经过高数值孔径透镜聚焦后，在焦场会形成很强的纵向电场或磁场分布。基于这些特性，圆柱矢量偏振光束在超分辨显微镜技术，粒子捕获技术，原子导引技术和材料加工等技术领域有着广泛的应用。而且，在加工材料时往往需要高能量、短脉冲光源，因为短脉冲有利于降低材料的熔覆阈值和提高加工精度。这些因素促进了对具有高峰值功率和短脉冲宽度的矢量偏振光的需求。 矢量偏振光束可通过在激光器谐振腔内置入偏振选模元件，从而形成激光振荡，直接输出矢量偏振光束。众所周知，以稀土掺杂光波导为增益介质的光纤激光器由于其功率可扩展性好，散热效果好，模式约束力强，吸引了科研人员越来越浓的兴趣。迄今为止已经有许多课题组研究产生矢量偏振光束的光纤激光器，然而，所获得的功率和效率通常都不高。少数矢量偏振光纤激光器的功率效率较高，但是核心器件的制造成本太高，不利于进一步推广和产业化。为了克服长久以来矢量偏振光纤激光器输出功率低、效率低和成本高的劣势，本论文提出并采用了将单透镜成像系统与双折射走离结合起来的选模机制，成功实现了高功率、高效率和极低成本的矢量偏振光纤激光器。基于此选模机制，首先我们成功实现高效率、高功率的连续输出的矢量偏振掺镱光纤激光器，在此基础上，分别采用Cr4+:YAG晶体和半导体可饱和吸收镜（SESAM）作为被动调Q元件，实现了被动调Q的矢量偏振光纤激光器。实验证明，这种将单透镜成像系统和双折射走离结合起来的选模机制可有效简化谐振腔结构，使激光器形成高功率、高效率的矢量偏振激光振荡，同时极大地降低了矢量偏振光纤激光器的成本。 本论文的主要内容如下： 第一章，简要介绍了径向和切向偏振矢量光束，并根据光纤模式理论模拟了这两种光束在光纤中的强度分布情况。然后，我们介绍了矢量光束的潜在应用价值。接着，我们总结了产生径向和切向矢量光束的方法。最后概括了本论文的主要内容。 第二章，将单轴晶体和单透镜组合作为选模机制引入激光器谐振腔，成功实现了高效率、高功率和切向偏振的连续振荡掺镱光纤激光器。在研究中，首先根据双包层光纤激光器速率方程理论对激光器进行了数值模拟，获得了小信号增益分布和激光器输出特性；其次，在实验中采用c切YVO4和单透镜的组合选模，从掺镱光纤激光器中获得切向偏振光束输出，输出最大功率可达3.94 W，输出斜效率约为71%。该激光器结构简单紧凑，成本低，实验结果证明了偏振选模机制用于矢量光纤激光器功率标定的可行性。 第三章，基于单轴晶体和单透镜组合的选模机制，成功实现了基于Cr4+:YAG可饱和吸收晶体的被动调Q切向偏振掺镱光纤激光器。在研究中，Cr4+:YAG晶体仅单面镀膜，同时被用作可饱和吸收体和输出耦合镜；其次，单轴晶体和单透镜组合的方案既能用于偏振分光又利于可饱和吸收体饱和。该激光器谐振腔结构简单且损耗较少，它发射高功率的切向偏振脉冲光束，最高斜效率为72.6%，最高平均输出功率为4.11 W。在最大吸收泵浦功率6.4 W下，激光脉冲持续时间为132 ns，脉冲重复频率为112 kHz。该实验进一步证明了单轴晶体和单透镜组合的选模机制有利于高效率、高功率矢量偏振掺镱光纤激光器的被动调Q运转。 第四章，基于单轴晶体和单透镜组合的选模机制，成功实现了基于SESAM的被动调Q径向偏振掺镱光纤激光器。在实验中，利用c切YVO4和单透镜的组合选模，采用SESAM作为可饱和吸收体，分别实验研究了采用线型腔和折叠腔的被动调Q激光器。在线型腔结构时，光纤激光器发射调Q脉冲，激光功率达到3.6W，斜效率为68.7%。在折叠腔结构时，光纤激光器发射径向偏振调Q脉冲，激光功率为637 mW，斜效率为14.1%，在吸收泵浦功率6.4 W时，激光脉冲持续时间为300 ns，脉冲重复频率为454.5 kHz。 第五章，对本论文的研究结果进行了总结，指出实验中的不足之处，并提出了可能的解决方案。 |
| 英文摘要 | Radially and azimuthally polarized light beams, being two eminent members of cylindrical vector light family, are characterized by spatially axis-symmetrical polarizations and doughnut-shaped intensity patterns, and they have shown the particular features and advantages over linearly or circularly polarized beams. For example, they can be tightly focused and form longitudinal electric or magnetic fields at the focal spot. Owing to these factors, cylindrical vector beams have been applied widely in many fields, including high-resolution microscopy, particle trapping, atom guiding, material processing, etc. Furthermore, the material processing usually requires a laser source that emits energetic and short-duration light pulse for the sake of the ablation threshold of material and also high precision. These factors impel a great demand for the pulsed and vectorized laser source. Among various vector lasers, the rare-earth doped fiber laser has attracted increasing interest owing to its capacities for power scaling, thermal dissipation and modal confinement. So far some researches had already produced fiber lasers with vector polarized light beams. However, the obtained output powers and slope efficiencies ware not ideal. A few vector fiber lasers with high output power and slope efficiencies ware costly, which was not helpful for the development of industrialization. In the study, we proposed to use the combination of a birefringent crystal and single-lens image system as the polarization discrimination. With the proposed scheme, we introduced a piece of c-cut yttrium vanadate (YVO4) crystal and s single lens in the laser cavity, and demonstrated successively a continuous-wave and azimuthally polarized ytterbium-doped laser, and thereafter developed two passively Q switched versions of this vector fiber laser by using Cr4+:YAG and semiconductor saturable absorber mirror (SESAM) as the saturable absorbers (SAs), respectively. In these experiments, the laser showed high power and extremely high efficiency and the cost of it was quite low, these results verified that our scheme simplified significantly the configuration of laser cavity, and beneficial to the vector laser with high power and high efficiency. The layout of the dissertation is as follows: In chapter one, we overviewed the background of radially polarized and azimuthally polarized vector beams and simulated the intensity distribution of these beams based on optical fiber-mode theory. Then we introduced the potential application. After that, we summarized the methods to generate radially polarized and azimuthally polarized vector beam. Finally, we present our scheme to realize the continuous wave and Q-switched vectorized ytterbium-doped fiber lasers. In chapter two, by using the proposed mode discrimination mechanism, an ytterbium-doped fiber laser was demonstrated to emit azimuthally polarized light with high laser power and efficiency. In the study, firstly, the numerical model of the double-clad fiber laser was built based on the rate equations. The small signal gain distribution and output characteristics of double-clad fiber laser were simulated. Further, a c-cut YVO4 crystal and a single-lens imaging system was introduced into the laser cavity of an ytterbium-doped vector fiber laser. With this simple, compact and low-cost scheme, the fiber laser emitted azimuthally polarized light, and the laser power reached 3.94 W with a high slope efficiency of ~71%. This result presented an experimental evidence of low-cost birefringent mode discriminator for power scalability of vector fiber laser. In chapter three, we demonstrated an azimuthally polarized and passively Q-switched Yb-doped fiber laser. In the study, a single-side coated Cr4+:YAG crystal was used as SA and also output coupler. The combination of a birefringent crystal and a single lens was used for vector mode selection and it also favored the saturable absorption of SA. For the simplicity and low optical loss of the resonator cavity, this fiber laser emitted azimuthally polarized pulse with a high slope efficiency of 72.6% and high average power of 4.11 W. The laser pulse had 132-ns duration and 112-kHz repetition rate at the absorbed pump power of 6.40 W. In chapter four, we demonstrated a passively Q-switched Yb-doped fiber laser by using a SESAM as SA, and also the combination of a birefringent crystal and a single lens was used for vector mode selection. In the linear cavity configuration, the fiber laser emitted Q-switched pulse with an average power of 3.6 W and a slope efficiency of 68.7%. In the folded cavity configuration, the fiber laser emitted radially polarized pulse with a slope efficiency of 14.1% and average power of 637 mW. The laser pulse had 300 ns duration and 454.5 kHz repetition rate at the absorbed pump power of 6.40 W. In chapter five, the results were summarized, and the prospect of vector fiber laser was discussed. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/16885]  |
| 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 | 邹琳. 基于内腔双折射选模机理的高效、高功率矢量偏振掺镱光纤激光器研究[D]. 中国科学院上海光学精密机械研究所. 2015. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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