| 题名 | 大口径钕玻璃片放大自发辐射若干问题研究 |
| 作者 | 王冰艳 |
| 学位类别 | 博士 |
| 答辩日期 | 2016 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 朱健强研究员 |
| 关键词 | 片状放大器，钕玻璃，放大自发辐射，包边结构，亚表面缺陷 |
| 其他题名 | Research on Amplified Spontaneous Emission of Large-Aperture Neodymium Phosphate Glass Disk |
| 中文摘要 | 为了获得大能量输出的 ICF 驱动器同时满足元件的抗激光损伤阈值要求， 发展大口径的放大器势在必行。棒状放大器在口径增大到一定程度时会出现泵 浦困难，增益不均匀等问题， 因此片状放大器必然是 ICF 驱动器中所选择的主 放大器类型。钕玻璃是片状放大器最常用的增益介质，其增益能力直接决定了 片状放大器的能量输出。 随着通光口径的不断增大，放大自发辐射（ ASE）和 寄生振荡（ PO）对钕玻璃片储能的影响越来越显著， 也是钕玻璃片及片状放大 器口径增大的主要限制因素。 ASE 在增益介质中传输一旦形成闭合回路，且增 益大于损耗即形成 PO。 一旦抑制了 ASE，配合增益介质切小斜角， PO 能够得 到有效的抑制。强 ASE 有两个途径，其一为高增益，与片状放大器能量转换过 程有关；其二为长路径，一般采用侧面包边结构截断， 包边结构界面处一般包 含三种光学现象，透射，反射，散射， 其中透射和反射与包边剩余反射率有关， 散射则由加工缺陷产生， 其存在影响了包边结构的 ASE 抑制能力。 因此本文从 这两个方面探寻抑制 ASE 的方法，对发展更大口径的片状放大器有重要意义。 本文的研究内容主要有： 1.本文首先概述了使用片状放大器的意义，从片状放大器构型，增益介质 总类及形状等方面简述了片状放大器的发展成果。其次概述了为抑制钕玻璃片 ASE 和 PO 而发展的包边结构，论述了各种包边结构的优缺点。 2.在神光 II 主放大器参数条件下，采用蒙特卡洛和光线追迹算法构建了考 虑 ASE 时钕玻璃片三维储能分布程序，计算了包边完全吸收时，储能分布随泵 浦时间的变化关系， 计算结果与文献报道结果相同。计算了考虑包层剩余反射 率为 0.05%时，增益介质泵浦结束后的平均小信号增益系数为 4.1305m-1，并与 采用探针法测量的平均小信号增益系数进行了对比。计算了不同剩余反射率时 小信号增益系数和增益均匀性的变化， 计算结果表明， 对于通光口径为 310mm 的钕玻璃片， 剩余反射率大于 0.1%时小信号增益系数和增益均匀性显著下降。 受激发射截面增加虽然能够增加小信号增益系数但会导致增益均匀性下降。 随 着泵浦作用时间增加，小信号增益系数和增益均匀性下降，因此，在保证氙灯 工作在临界阻尼状态下时应尽量减少泵浦作用时间。 在现有初始储能密度情况 下， 增大口径意味着增益能力下降，大口径下要获得现有增益能力需要增大初 始储能密度。 3.包边结构是大口径钕玻璃片中抑制 ASE 的主要途径，然而钕玻璃侧面一 般采用铣磨加工（ 数控加工的一种），较多的亚表面缺陷残留在加工后材料的表 层，降低了包边结构抑制 ASE 的能力。全面分析了研磨抛光中的亚表面缺陷类 型，根据力与材料的应力作用对缺陷进行了建模，并提出等效剩余反射率以定 量地描述加工后亚表面缺陷对钕玻璃片增益的影响。采用 FDTD solutions 计算 了加工过程中的典型缺陷不同角度入射时的散射特性，并进行了散射测量实验。 以数控加工（ CNC） 抛光中形成的主要缺陷塑性形变型为例，在 c 类单网格区 域内，缺陷数大于 50 时， 对于口径为 310mm 钕玻璃片包边结构， 剩余反射率 由 0.05%增大至 0.1%，引起增益下降。针对加工缺陷散射，对 CNC 加工后的 钕玻璃侧面酸洗 15 分钟并镀增透膜有助于减少缺陷散射，并进行了实验验证。 据此提出了 2 种改进的包边结构。 一种在原有包边结构中增加了钕玻璃侧面酸 洗并镀膜操作，另一种直接采用薄膜作为无机粘剂将激光玻璃和包边玻璃粘合 起来。后者不仅减缓了侧面加工缺陷散射，且避免了原包边结构中使用的有机 包边胶在高氙灯辐照下易分解脱落耐候性较差等问题。 4.针对提出的采用薄膜作为无机粘剂包边方法，从键合的角度探索了实现 方案。首先调研了已有的各种键合方法及其键合机理。 低温键合法，即氢氧化 物催化键合方法具有键合温度低，透光性较好，结构稳定等优点，是一种实现 无机粘剂包边的可行方法。基于氢氧化物催化键合提出了低温激光玻璃键合包 边方法，并根据此方法选取不同键合溶液制作了钕玻璃键合样品，进行了氙灯 辐照实验。 采用 NaOH 水溶液并进行加压处理， 及采用硅酸钠水溶液制成的键 合样品在 2000 发次均未出现炸裂， 初步验证了这种方法的可行性。 |
| 英文摘要 | The development of large aperture amplifier is necessary to obtain an inertial confinement fusion (ICF) laser facility with high output power and meeting the requirement of the laser induced damage threshold. For a lager-diameter rod amplifier, the center of the rod surface is difficult to be pumped, and a inhomogeneous gain occurs, so disk amplifier is the main amplifier in an ICF laser facility positively. Neodymium phosphate glass (Nd:glass) is the typical gain medium which determines the gain of disk amplifier directly. With the increase of clear aperture, amplified spontaneous emission (ASE) and parasitic oscillation (PO) have been the key limiting factors to the diameter of Nd:glass and disk amplifier. ASE transmits in a disk, when a circuit forms and the gain is bigger than loss PO occurs. Once the ASE is restricted, and symmetry of disk is destroyed, PO could be restricted effectively. A strong ASE occurs with a high gain and long path. A high gain relates to the energy conversion in disk amplifier. A cladding structure is employed to cut the long path. The boundary in the cladding structure contains three optical phenomena: reflecting, refracting and scattering. Reflecting and refracting relate to the residual reflectivity of cladding structure, while scattering has relationship with processing defects which influence the suppression of ASE in cladding structure. Therefore, simulations and experiments are proposed to suppress ASE from these two aspects. The main work and achievements are as follows: 1.Firstly, the development of disk amplifier is discussed from the cavity structure and the gain medium. The cladding structures which have developed for the suppressing of ASE is summarized and the advantage and disadvantage of cladding structure are discussed. 2.Using the parameters of the disk amplifier in SG-II facility, a three dimension model with Monte Carlo and Ray tracing algorithm which can be used to calculate the gain distribution with different pumping time is built. The gain evolution in the light pass surface in different pumping time is calculated when the residual reflectivity is assumed to be 0%, which shows the same trend with the previous articles. When the residual reflectivity is assumed to be 0.05%, the average small signal gain coefficient in the disk is calculated to be 4.1305/m with this model and this result has been compared with the average small signal gain coefficient measured with the probe method. The small signal gain coefficient and gain uniformity decrease sharply when the residual reflectivity is bigger than 0.1% for the Nd:glass with the clear aperture of 310mm. A bigger small signal gain coefficient and a decreasing gain uniformity can obtain with bigger simulated cross section. When the pumping time increases, the small signal coefficient and the gain uniformity will decrease. So the pumping should be small when the critical damping is satisfied. When the clear aperture is increased, the gain decreases for recent initial storage energy. 3.Cladding structure is the main way to suppress ASE. The side of the Nd:glass is processed by computer numerical control (CNC), and large subsurface defects exists after processing, which decreases the suppressing of cladding structure. An equivalent residual reflectivity of cladding structure is proposed to assess the influence of defects to the gain of Nd:glass. The subsurface defects are modeled based on the interaction of material and power. The subsurface defects scattering at different incident angles are calculated quantitatively using FDTD solutions and experimentally. For the typical subsurface defects after CNC and the Nd:glass with a clear aperture of 310mm, the residual reflectivity can be improved to be 0.1% with 50 defects in c single gridding, and thus the gain decreases. Etching for 15 minutes and coating are proposed to decrease the subsurface defects scattering on the side of the Nd:glass after CNC to improve the quality of cladding structure, and which are verified by experiment. Two improved cladding structures are put forward. In the first structure, an etching and coating is added on the side of Nd:glass, then the Nd:glass is adhered to the cladding glass with glue. In the second structure, a anti-reflection film is employed instead of organic glue. The improved structure can avoid the decomposing, falling off in the high flash-lamp irradiation, which makes the life of the cladding structure improved. 4.From the perspective of bonding, a low temperature bonding method, which is also named Hydroxide-Catalysis bonding, is proposed to realize the cladding structure mentioned in the upper chapter, based on analyzing the bonding mechanism of different bonding method. Using this bonding method, samples are bonded with different bonding solutions and the bonded samples are placed in the high flash-lamp irradiation environment. For samples bonded with NaOH solutions under pressure, and the sodium silicate solutions, no break and falling off are observed more than 2000 shots. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15975]  |
| 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 | 王冰艳. 大口径钕玻璃片放大自发辐射若干问题研究[D]. 中国科学院上海光学精密机械研究所. 2016. |
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