三倍频激光诱导损伤及光束质量控制研究
文献类型：学位论文
| 作者 | 郭亚晶 |
| 学位类别 | 博士 |
| 答辩日期 | 2014 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 林尊琪 |
| 关键词 | 光束质量控制 激光诱导损伤 横向受激拉曼散射 近场辐照损伤测试 灰度抑制分水岭标记算法 KDP晶体 |
| 其他题名 | researches of laser-induced damage and beam quality control at 351nm |
| 中文摘要 | 对于大口径高功率激光系统，三倍频激光诱导损伤和大口径KDP晶体中横向受激拉曼散射(TSRS)是严重影响光束质量和威胁系统安全运行的重要因素。由于激光诱导损伤受材料性质、激光参数及不同损伤机制等多种因素影响，需要良好的理论依据和大量的实验数据来深入探讨和完善激光诱导损伤研究；而TSRS效应对增益系数非常敏感，有必要对拉曼散射光进行直接测量来评价TSRS效应。因此，研究能够准确测试元件损伤性能及TSRS增益系数直接测量的技术途径和方法对三倍频激光光束质量控制有重要意义。 本文针对三倍频激光诱导损伤测试和大口径KDP晶体中横向受激拉曼散射(TSRS)增益系数测量展开全面研究，一方面提出结合近场辐照和带有灰度抑制分水岭标记图像分割算法的损伤测试方法，建立相应损伤测试平台进行损伤测试实验，获得了熔石英样品激光照射下的损伤阈值、损伤增长系数及损伤点分布情况，为认识激光诱导损伤机理及损伤规律提供实验手段支持；另一方面，通过改进影响测量精度的关键技术，建立了TSRS增益系数直接测量装置，直接获得拉曼散射光时间波形和相应增益系数。论文的主要内容和创新点包括： 1、基于已有的光学元件表面缺陷对光束复振幅调制模型，分析了元件表面损伤点对351nm激光传输过程中光束质量的影响。得到了不同损伤点位相调制深度下，351nm激光在空气和熔石英介质中传输时的光场分布情况；最后，计算了不同损伤点空间分布对激光传输过程中光束质量下降的影响。得到了近场填充因子下降到50%时对应的损伤点尺寸，以及光束继续在熔石英介质中传输时光场最大值不明显增加的安全距离。 2、首次提出了将激光近场辐照与带有灰度抑制分水岭标记图像分割算法相结合的损伤测试方法。该方法解决了全光斑内损伤点同时检测过程中因照明不均匀和显微镜放大倍率低等因素引起的损伤图像过分割现象，得到较好的损伤点尺寸信息提取效果。 3、定义了基于近场辐照方式的损伤阈值，并搭建损伤性能测试实验平台，获得了Corning-7980熔石英样品在3ns、351nm单波长激光照射下的损伤阈值和指数增长系数分别为2.94±0.57J/cm2和1.10±0.31，以及在1ns、多波长激光照射下的损伤阈值和指数损伤增长系数分别为8.22±2.87J/cm2和0.59。同时获得辐照光斑内损伤点尺寸分布情况，发现小尺寸损伤点数量明显高于大尺寸损伤点数量，损伤点数量随着损伤点横向尺寸增加迅速下降。 4、通过改进谐振腔设计、拉曼散射光分离及提取、杂散光管理等影响增益系数测量精度的关键技术，建立大口径KDP晶体中TSRS增益系数直接测量装置。该装置利用小尺寸晶体样品、腔式振荡结构离线进行增益系数测量，利用351nm激光泵浦KDP晶体产生拉曼散射光，通过直接测量散射光时间波形，获得KDP晶体中TSRS增益系数goo=0.28±0.02cm/GW。 |
| 英文摘要 | For the large-aperture and high power laser system, the laser-induced damage and transverse stimulated raman scattering effect are the major factors of affecting the beam quality and threatening the opertation security of laser system. Because the laser-induced damage is affected by material properties, laser parameters and damage mechanism, a good theory and mass of datas are necessary for investigating the laser-induced damage characteristic. And, the transverse stimulated raman scattering effect is sensitive to the scattering light gain coefficient. It’s necessary to directly measure the coefficient. Therefore, the researches of laser-induced damage property test methods and TSRS gain coefficient measurement technology are significant to the beam quality control at 351nm. Aiming at the researches of laser-induced damage test at 351nm and TSRS gain coefficient measurement in large-aperture KDP crystal, this paper proposes the damage test method combining the near-field irradiation and marker-based watershed algorithm with gray control. And the corresponding experimental facility is set up to conduct the damage property tests. Then, the damage threshold, the damage growth coefficient and damage site size distribution are obtained for the fused silica samples. It provides the technical assistance for the investigation of laser-induced damage mechanism and damage rules. In addition, by improving the key technologies affecting the measurement accuracy, the direct measurement device for TSRS gain coefficient is estabilished, which directly obtains the temporal pulse of raman scattering light and the corresponding gain coefficient. The main contents and innovative results include the following aspects: 1、Based on the existing modulation model of optical surface defects on the beam complex amplitude, it analyzes the effects of damage sites on the transmitted beam quality at 351nm. For the different phase modulation depths, the transmitted laser fluence distributions in the air and fused silica are obtained. Finally, it analyzes the effect of damage site morphology on the beam quality degradation induced by the phase modulation of damage site. On the basis above, the maximum damage site size and its safe transmission distance in the fused silica are determined when the near-field fill factor decreased to 50%. 2、This paper first proposes the damage test method combining the near-field irradiation and marker-based watershed algorithm with gray control. It suppresses the damage image over-segmentation problem for the simultaneous detection of damage sites inside the beam aperture, which results from the non-uniform illumination and low magnificantion of microscope. The results indicate that the damage site information extracted by marker-based watershed algorithm with gray control is credible. 3、Based on the near-field irradiation, a new defination of damage threshold is proposed that the threshold is the local fluence corresponding to the critical position of damaged area and non-damaged area. And, the damage test device is set up to measure the damage properties of fused silica samples. For the 351nm laser irradiation at 3ns, the damage threshold and growth coefficients of Corning-7980 sample are 2.94±0.57J/cm2 and 1.10 ± 0.31, respectively. For the multi-wavelength laser irradiation at 1ns, the damage threshold and damage growth coefficient of Corning-7980 sample are 8.22 ± 2.87J/cm2 and 0.59, respectively. Besides, the damage site size distribution is obtained. The results show that the damage site number with small size is apparently more than that with large size. Namely, the damage site number rapidly decreases with the increase of damage site size. 4、A direct measurement device of TSRS gain coefficient is established by improving the key technologies of resonant cavity design, the separation and extraction of raman scattering light, noise management, which affect the measurement accuracy. TSRS are generated from a KDP crystal pumped by 351nm laser. The TSRS gain coefficient is measured as goo=0.28±0.02cm/GW by measuring the temporal pulse of raman scattering. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15889]  |
| 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 | 郭亚晶. 三倍频激光诱导损伤及光束质量控制研究[D]. 中国科学院上海光学精密机械研究所. 2014. |
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。