端面泵浦径向偏振固体激光器
文献类型：学位论文
| 作者 | 夏克贵 |
| 学位类别 | 博士 |
| 答辩日期 | 2012 |
| 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 | 径向偏振激光 声光调Q 被动调Q 键合Nd:YAG 激光晶体 |
| 其他题名 | End-pumped and Radially Polarized Solid-state Laser |
| 中文摘要 | 径向偏振光是一种光强和偏振分布具有轴对称性的空心光束，可以应用于许多领域，如光镊、光存储和高分辨显微等。径向偏振光束在激光金属加工中也有重要应用前景，可用于金属激光切割、焊接以及打孔。由于径向偏振光的电矢量始终与切割刃垂直，与切割方向无关，有很高的菲涅尔吸收，可以获得更高的加工效率。利用激光器直接输出高功率、高偏振纯度的径向偏振光的相关研究引起广泛关注。本论文研究工作主要包括基于键合型激光晶体的径向偏振激光器（利用光子晶体光栅镜作为径向偏振输出耦合镜）的实验研究，以及基于内腔双折射晶体（c-切矾酸钇）的径向偏振激光器实验研究。本论文布局如下： 第一章，总体阐述了径向偏振激光的背景知识，回顾了目前产生径向偏振激光的各种技术方案，介绍了径向偏振激光的应用前景，最后提出了本论文的研究方向以及采用的技术方案。 第二章，由于薄片激光晶体在强泵浦下热效应严重，限制了薄片径向偏振激光器功率的提升，为解决此问题，我们采用键合结构晶体作为激光增益介质来抑制热效应。本章对基于键合结构的Nd:YAG激光晶体的连续径向偏振激光器进行了理论及实验研究，通过使用两端带不掺杂端帽的Nd:YAG键合结构晶体来削弱激光晶体中的热透镜效应，以光子晶体光栅镜为偏振选择器件，搭建了径向偏振连续激光器，有效克服了强泵浦时出现功率饱和下降的现象，获得了1.29W的径向偏振激光输出，斜坡效率为46.5%，偏振纯度为97.9%。 第三章，调Q技术和径向偏振技术的结合可以获得短脉宽、高峰值功率的径向偏振激光，在前期薄片径向偏振脉冲激光器的研究中，由于薄片激光晶体在强泵浦下热效应严重，限制了薄片径向偏振激光器功率的提升，在强泵浦作用下，出现功率饱和的现象。本章我们采用热传导能力较强的键合结构晶体来改善激光器性能，分别搭建了基于声光Q开关的主动调Q和Cr4+:YAG被动调Q径向偏振脉冲激光器。在主动调Q径向偏振激光器的研究中，获得的脉冲重复频率可在500赫兹到9.238千赫兹间连续可调，脉冲宽度在26.4纳秒到67.2纳秒之间，脉冲峰值功率最高达到7.75千瓦。而基于可饱和吸收体Cr4+:YAG的被动调Nd:YAG径向偏振激光器在不加外部主动冷却的情况下，获得了稳定的脉冲输出，脉冲重复频率在13.9千赫兹时，脉冲宽度为18.9纳秒，平均输出功率383毫瓦，脉冲峰值功率为1.457千瓦，光束偏振纯度高达97.6%。 第四章，实验研究了利用双折射晶体（c切矾酸钇）作为腔内起偏元件的Nd:Y AG径向偏振激光器，以及利用c切掺钕矾酸钇同时作为激光增益介质和腔内起偏元件的Nd:YVO4径向偏振激光器。该方法基于晶体双折射特性，利用o光和e光的光程差异，简单调整透镜到谐振腔前腔镜的距离使e光稳定振荡产生径向偏振输出。输出的径向偏振光束即使在功率很低的情况下也非常稳定，该方法的简易性使其在径向偏振激光的研究中有重要前途。在以c切矾酸钇作为腔内起偏元件的Nd:YAG径向偏振激光器中，当输入泵浦功率15W时，获得输出功率为15.3毫瓦、偏振纯度为93.5%的径向偏振光输出；在c切掺钕矾酸钇同时作为激光增益介质和腔内起偏元件的Nd:YVO4径向偏振激光器的研究中，当腔长101.5毫米、输入泵浦功率7.35W时，获得63.8mW、偏振纯度为85%的低阶径向偏振光输出，而当腔为157毫米、输入泵浦功率6.88W时，获得出功率30.1mW的次高阶模径向偏振光输出。 |
| 英文摘要 | Radially polarized beams are characterized by annular shape and axial symmetry in both amplitude and polarization along the beam axis. Such beams are important for several applications, such as orientation of single molecules, optical tweezers, particles manipulation, optical data storage and resolution-enhanced microscopy. They are also suggested to use in metal processing, including metal cutting, welding as well as drilling. In material-processing application, the electric field vector of the radial-polarization irradiation is spatially perpendicular to the cutting front irrespective of the direction of cutting, which results in the high Fresnel absorption of metal material and thus ensures a very high overall efficiency. And now, many attentions focused on the generation of the radially polarized beam from a laser resonator with high efficiency, high power and high polarization purity. In this dissertation, we firstly described experimental study on continuous and pulsed operations of radially polarized solid-state laser based on bonded Nd:YAG laser crystal with photonic crystal mirror as polarization-selective output coupler. Thereafter we introduced another Nd:YAG laser with the utilization of c-cut YVO4 crystal as intracavity polarization component. The layout of the dissertation is as follows: In chapter 1, we overviewed the background of radially polarized vector beam, and then gave a summary on the ways to generate it as well as its related applications. We also depicted our proposals on fabricating the radially polarized lasers with bonded Nd:YAG laser crysal by applying either photonic crystal grating mirror or birefringent uniaxial crystal as intra-cavity polarization-selective element.. In chapter 2, the output power of the micro-chip radially polarized laser was limited due to the strong thermal effects of the lasing material at intensive pumping. A bonded Nd:YAG crystal is chosen as the lasing material which is bonded by two un-doped YAG end caps and the high thermal conductivity of this bonded structure could weaken the temperature gradient in the lasing area and thereafter the thermal lens effect at the presence of intensive pumping. Firstly, we analysed theoretically on thermal effects of the lasing crystal with different boned structures of laser gain crystal based on spatially three-dimensional heat transfer model. Furthermore, we reported the experimental study on the composite Nd:YAG crystal laser with employing the photonic crystal grating as the output coupler. The radially polarized output from this laser reached 1.29-W laser power with a slope efficiency of 46.5% and a polarization purity of 97.9%. In chapter 3, as Q switching allows the production of high-peak-power pulses, the association of the radially polarized oscillation with Q switching in one laser resonator could become a preferred option for the high-field applications of radial polarization. While in the previous research on microchip pulsed radially polarized laser, the output power was limited due to the strong thermal effects of the lasing material at intensive pumping. In this study, we presented two pulsed, radially polarized lasers Q-switched by either acoustic-optic modulator (AOM) or saturable absorber. Firstly, we presented an laser-diode end-pumped, actively Q-switched and radially polarized Nd:YAG laser by using the AOM as the active Q switch. The laser generated pulses of 26.4-67.2 ns duration and the repetition rate could be continuously adjusted from 500Hz to 9.238 kHz with peak power up to 7.75 kW. Secondly, we presented a radially polarized and passively Q-switched Nd:YAG laser by utilizing a Cr4+:YAG crystal as the saturable absorber. The averaged laser power reaches 383 mW with a slope efficiency of 33 %. The laser pulse has 1457 W of peak power, 18.9 ns duration, and ~97.6-% polarization purity at a 13.9 kHz repetition rate. In chapter 4, we presented an LD-end pumped, radially polarized laser by using a birefringent uniaxial crystal (c-cut YVO4 or Nd:YVO4) as intra-cavity polarization-selective element. The oscillation of radial polarization was based on the optical path difference between an extraordinary ray and an ordinary ray induced by the birefringence of the crystal. By simply adjusting the distance between the front cavity mirror and the intracavity lens, only the extraordinary ray became stable for the oscillation, resulting in the generation of a radially polarized beam. The beam obatained from this laser was very stable even at low power output and thus this laser is expected to be a promising radially polarized laser source because of its excellent simplicity. In the experiment of Nd:YAG laser by using a intra-cavity c-cut YVO4, we get a 15.3-mW radially polarized beam with a high polarization purity of 93.5% at input pump power of 15W. And in the experiment of Nd:YVO4 laser, when the cavity-length was 101.5mm, we get a 63.8-mW laser beam of radial polarization with a polarization purity of 85% at input pumped power of 7.35W, and when the cavity-length was 157mm, we get a higher-order mode radially polarized laser beam with a output power of 30.1mW at input pumped power of 6.88W |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15694]  |
| 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 | 夏克贵. 端面泵浦径向偏振固体激光器[D]. 中国科学院上海光学精密机械研究所. 2012. |
入库方式： OAI收割
来源：上海光学精密机械研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。