宽带“三明治”结构金属介质光栅和金光栅的激光损伤测试及其机理研究
文献类型：学位论文
| 作者 | 黄昊鹏 |
| 文献子类 | 博士 |
| 导师 | 邵建达 |
| 关键词 | 啁啾脉冲放大技术 Chirped Pulse Amplification technique “三明治”金属介质光栅 Sandwiched metal multilayer dielectric gratings 金光栅 Gold gratings 激光损伤 Laser damge |
| 其他题名 | Laser damage testing and damage mechanism of the broadband sandwiched metal multilayer dielectric gratings and gold gratings |
| 英文摘要 | 脉宽压缩光栅是啁啾脉冲放大(CPA)技术中的关键元件，随着拍瓦高功率激光装置的发展，脉宽压缩光栅抗激光损伤能力的提高至关重要，因此对光栅损伤机理研究的重要性就凸显出来。本文利用优化改进的飞秒激光损伤测试系统，针对宽带“三明治”结构的金属介质光栅/膜和金光栅/膜，进行了飞秒损伤测试。通过双温模型、热传导模型和热力耦合模型分析了金光栅及不同基底金膜的损伤机制；通过介电常数和联合离化模型分析了金属介质光栅的初始损伤机理；通过对金属介质光栅电场、温度和应力的分布分析了皮秒激光脉冲作用下的损伤机理。本文主要内容如下： 1. 针对目前飞秒损伤测试系统中存在的测量误差大、测量精度不高等缺点，对飞秒损伤测试系统进行了改进，加入了自主研制的偏振片及λ/2波片，并且通过等效距离测光斑的方法使误差从13%降低到3%，提高了测量精确度。 2. 通过中心波长为800 nm，脉宽为31 fs的激光损伤测试系统对金光栅的飞秒单脉冲和多脉冲损伤测试，我们发现初始损伤均为鼓包，并且鼓包高度随着脉冲数的增加而变大，损伤阈值从0.35 J/cm2降低到0.10 J/cm2。通过扫描电子显微镜细微的观测我们发现了微孔是影响金光栅损伤阈值的主要因素，并且通过理论模拟分析验证了激光可以通过微孔与下层光刻胶发生作用产生热冲击使金膜层脱离光刻胶形成鼓包形貌，提出了采用磁控溅射工艺制备的金光栅有利于损伤阈值的提高。 3. 通过电子束蒸发工艺制备的光刻胶基底金膜和熔石英基底金膜的飞秒损伤对比，发现熔石英基底的金膜具有更高的抗激光损伤能力，损伤阈值为0.64 J/cm2，损伤形貌表现为熔融烧蚀；而光刻胶基底金膜损伤阈值为0.30 J/cm2，损伤形貌表现为鼓包突起。通过电场，双温模型，热力耦合模型对损伤机制进行了分析，并基于结合力测量结果提出了金膜与基底材料的结合力是限制光栅损伤阈值提高的主要原因。指出采用直接在基底上刻蚀光栅结构，再镀制金膜的光栅具有更强的抗激光损伤能力。 4．对“三明治”结构的金属介质光栅进行了飞秒损伤测试，通过扫描电子显微镜和聚焦离子束刻蚀的观测，首次确定了“三明治”光栅的初始损伤位于HfO2层。通过介电常数和联合离化模型分析了三明治结构金属介质光栅的飞秒初始损伤机制及损伤的发展，指出三明治结构中的HfO2是限制金属介质光栅阈值提升的主要因素，为进一步提高金属介质光栅抗激光损伤能力提供了有利的参数依据。 5. 对“三明治”结构的金属介质光栅进行了皮秒损伤测试，通过扫描电子显微镜和聚焦离子束刻蚀的观测，发现初始损伤位置与飞秒初始损伤不同，皮秒初始损伤位于金膜层。通过温度分布和应力分布计算，得出金膜层由于其金属本身具有的吸收性质，会吸收大量的入射激光能量，使金膜达到一个很高的温度，由于热力耦合作用，应力的分布主要也在金膜层，并且最大应力位置与温度最高位置相一致。随着时间的推移，膜层间会通过相互作用释放金膜层中的温度和应力，并且温度和应力释放的方向会沿着光栅结构中薄弱之处发展。; The pulse compression gratings are one of the most critical optical elements in the chirped-pulse amplification technique. The improvement of laser damage resistance of pulse compression gratings is critical important with the development of high power laser facilities. Therefore, the importance of research on grating damage mechanism is highlighted. In this paper, the femtosecond laser damage test system is optimized. The femtosecond-laser-induced damage behaviors of metal multilayer dielectric gratings (MMDG) and gold gratings for pulse compression are explored. The damage mechanism of gold gratings and gold film with different substrates is analyzed by two-temperature model (TTM), heat conduction and thermodynamic coupling model. Femtosecond laser-induced damage initiation mechanism on metal multilayer dielectric gratings is researched by dielectric constant and the plasma corresponding kinetic rate equation. Picosecond laser-induced damage mechanism on metal multilayer dielectric gratings is also researched by calculating the distribution of electric field, temperature and stress. The main contents of this paper are as follows: 1. The femtosecond laser damage test system is optimized by adding a broadband half-wave plate and two broadband reflective polarizer, which reduced the measurement error and improved the measurement accuracy. The spot measurement accuracy is improved by equivalent distance measurement. 2. Au-coated gratings (ACGs) for chirped pulse compression were irradiated using 800 nm multiple laser pulses with duration of 31 fs. The laser-induced damage threshold (LIDT) of Au-coated gratings decreases from 0.35 J/cm2 to 0.10 J/cm2 with the increased pulse shots. The near threshold damage feature of Au-coated gratings at different pulses shows blisters. It is indicated that the gradually increased blister height with increasing multiple pulses on ACGs is caused by the accumulation effect. The damage morphologies combine with simulated results indicate that the damage of the ACGs can be attributed to the pinholes at the base of grating pillars and the separation of gold coating and photoresist gratings caused by the photoresist absorbed the incident laser energy. Therefore, we consider the damage threshold can be enhanced by optimizing coating deposition technology to reduce pinholes density and increase the adhesion between the gold and the photoresist. 3. Gold films on two different types of substrates were fabricated by electron beam (e-beam) evaporation, and their femtosecond laser-induced damage properties were evaluated. The first sample was made of gold film deposited on fused silica, whereas the second consisted of gold deposited on photoresist. 1-on-1 damage tests were performed by using an 800 ± 35 nm laser with pulse duration of 31 fs. Different damage thresholds and morphologies were obtained for the two samples. The damage threshold of the gold film on fused silica was 0.64 J/cm2, with the typical damage morphology of thermal ablation and melting; the damage threshold of the gold film on photoresist was 0.30 J/cm2, with the typical damage morphology of blisters or peeling off. In order to better understand the impact of the substrate on the properties of the whole sample, the normalized electric field intensity, temperature, and thermal stress distributions were calculated. The adhesion between the gold film and substrate were measured and the experimental results well agreed with the theoretical expectations. The results indicate that gold films deposited onto grating-structured fused silica will have more powerful laser damage resistance performance. 4. The femtosecond-laser-induced damage behaviors of metal multilayer dielectric gratings (MMDGs) for pulse compression are explored. The ridge of this type of grating consists of a HfO2 layer sandwiched between two SiO2 layers. The initial damage position is on the HfO2 layer in an MMDG. The dielectric constant and the plasma corresponding kinetic rate equation is constructed to explain the femtosecond laser -induced damage initiation mechanism on the MMDG, and the model can simulate the evolution of the electron density in the conduction band and the change of the dielectric constants of HfO2 and SiO2 in the sandwiched grating structure. The dramatic increase in the imaginary part of the dielectric constant of the middle HfO2 layer indicates that it strongly absorbs laser energy, resulting in damage to the MMDG. The experimental results and theoretical calculation agree very well with each other. 5. The picosecond -laser-induced damage behaviors of metal multilayer dielectric gratings (MMDGs) for pulse compression are explored. The initial damage position is on the gold layer in an MMDG，which is different with the femtosecond initial damage position. Gold film layer can absorb large incident laser energy by calculating the temperature distribution and stress distribution. Therefore, gold film reached a very high temperature. The stress is mainly distributed in the gold film layer by thermodynamic coupling. The maximum stress position is consistent with the maximum temperature. The temperature and stress in the gold film layer will be released by the interaction between film layers. The direction of release will follow the weak position in the grating structure. Therefore, the picosecond damage of grating is caused by temperature and stress. |
| 学科主题 | 光学工程 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31097]  |
| 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 | 黄昊鹏. 宽带“三明治”结构金属介质光栅和金光栅的激光损伤测试及其机理研究[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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