高功率脉冲压缩光栅的激光损伤机制及其测试技术
文献类型：学位论文
| 作者 | 孔钒宇 |
| 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 | 贺洪波 晋云霞 |
| 关键词 | 脉冲压缩光栅 衍射光学 激光损伤 |
| 其他题名 | Laser-Induced Damage Mechanism and Testing Techniques of High-Power Pulse Compressed Gratings |
| 中文摘要 | 脉冲压缩光栅的研制进展推动着啁啾脉冲放大技术在超短、高能激光系统中的应用，但是脉冲压缩光栅的损伤测试技术和激光损伤机制仍有待深入研究。我们对中心波长1053nm皮秒全介质光栅、800nm飞秒全介质光栅和800nm飞秒金属介质光栅三种光栅样品进行激光单脉冲损伤破坏实验并对它们的损伤特性进行了研究，具体工作如下： 明确了光栅的初始损伤发生于光栅脊条背光面位置，与光栅近场强区分布相一致。 获得了脉宽为12ns的脉冲对两种工艺制作的1053nm皮秒全介质光栅的通量损伤阈值为分别为22J/cm2和23.7J/cm2。并发现光栅槽底为拱形结构，这样的结构导致了光栅槽底电场的增强，增加了光栅槽底发生灾难性损伤的风险。 用脉宽为0.5ps~9.7ps的激光脉冲在真空（5×10-4pa）和空气环境下对两种工艺制作的1053nm皮秒全介质光栅进行损伤实验，发现两种环境下光栅的损伤阈值和损伤形貌并没有显著差异。脉宽在0.56ps~49.5ps范围内，激光脉冲对1053nm皮秒全介质光栅的通量损伤阈值随着脉宽的增大遵循着τ0.26的规律，对应阈值从2J/cm2增加到6.8J/cm2。通过对光栅损伤形貌分析，认为光栅的损伤机制在脉宽10ps~20ps范围内开始发生转变。 脉宽在40fs~100fs范围内，激光脉冲对800nm飞秒全介质光栅的通量损伤阈值随着脉宽的增大遵循着τ0.25的规律从0.53J/cm2增加到0.75J/cm2。对光栅的损伤形貌进行分析，提出了光栅条内部平均场概念，以平均场值替代传统的最高强场计算导带电子数密度的演化过程，计算得到的理论损伤阈值与实验阈值相一致。用脉宽为40fs的激光脉冲对金属介质光栅进行损伤实验，获得该光栅的通量损伤阈值为0.32J/cm2，利用平均电场的联合离化模型计算得到该光栅的理论损伤阈值为0.36 J/cm2。 在对三种光栅损伤特征分析的基础上，用严格耦合波（RCWA）对光栅条横向损伤尺寸变化所引起光栅性能的变化进行了计算分析。发现当光栅条的横向损伤尺寸小于光栅条横向尺寸1/4时，1053nm皮秒全介质光栅仍具有较好的光学性能；当光栅条的横向损伤尺寸大于光栅条横向尺寸1/3时，800nm皮秒全介质光栅被认定为失效；对于金属介质光栅来说，光栅条的横向尺寸小于6nm时，仍然可以用于脉冲压缩。 |
| 英文摘要 | The investigation of pulse compression gratings (PCG) promotes the application of chirped pulse amplification (CPA) technology in the ultra-short, high energy laser system. But damage test techniques and the mechanism of laser damage of pulse compression gratings still needs to be further revealed. In this dissertation, three kinds of PCGs are involved, i.e., 1053nm picosecond all dielectric gratings, 800nm femtosecond all dielectric gratings and 800nm femtosecond metal multilayer dielectric gratings. Laser damage tests are carried out with single laser pulse. And laser damage characteristic of PCG is investigated. The main contents of the dissertation are shown as the followings: The damage morphologies of gratings indicate that the initial damages of the gratings occur on the grating lines at the opposite side of the illuminating beam, which coincide with the area of the high normalized electric field intensity (NEFI). The laser-induced damage of two kinds of 1053nm-picosecond all dielectric gratings is 22J/cm2 and 23.7J/cm2 for 12ns laser pulse, respectively. And we find that the bottom shape of the gratings is arched with a height of ~30nm, the arched bottom makes an enhancement of NEFI in groove bottom, thereby increasing the risk of catastrophic damage for the gratings. Laser damage tests for 1053nm-picosecond all dielectric gratings are carried out by 0.5ps~9.7ps laser pulse in vacuum (5×10-4pa) and air, respectively. It is found that the environment does not make a great change in LIDT of the gratings. The LIDT of the gratings enhances from 2J/cm2 to 6.8J/cm2 in pulse duration of 0.56ps~49.5ps, and the relationship of measured LIDT and the pulse durations resembles a power law τ0.26. Through the analysis of damage morphology, we consider that the damage mechanism of the gratings is changed in the pulse duration of 10ps~20ps. The LIDT of 800nm-femtosecond all dielectric gratings enhances from 0.53J/cm2 to 0.75J/cm2 in pulse duration of 40fs~100fs, and the relationship of measured LIDT and the pulse durations follows a power law τ0.25. Based on the analysis of damage feature, the average is proposed to calculate theoretical threshold based on electron production model via photoionization and avalanche ionization, which makes the theoretical and experimental results consistently. The LIDT of 800nm-femtosecond metal multilayer dielectric gratings is 0.32J/cm2 for pulse width of 40fs, and the theory LIDT of the grating is 0.36J/cm2. According to the damage characters of PCG, the influence of horizontal damaged size of grating ridge on optical properties of PCG is analyzed by numerical calculations using the rigorous coupled wave analysis (RCWA) method. Based on the evaluation criterion of valid PCG, the 1053nm-picosecond all dielectric gratings can offer a good optical performance when the horizontal damaged size is less than one quarter of whole horizontal length of grating ridge. For the 800nm-femtosecond all dielectric gratings, it can still be used for pulse compressed when the horizontal damaged size is less than one third of whole horizontal length of grating ridge. For the metal multilayer dielectric gratings, when the horizontal damaged size is less than 6nm, the gratings can still be used for pulse compression. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15857]  |
| 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 | 孔钒宇. 高功率脉冲压缩光栅的激光损伤机制及其测试技术[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
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