| 题名 | 飞秒激光照射引起玻璃结构变化的研究 |
| 作者 | 周秦岭 |
| 学位类别 | 博士 |
| 答辩日期 | 2004 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 干福熹 |
| 关键词 | 飞秒激光 玻璃 点缺陷 折射率 非线性电离 |
| 其他题名 | Femtosecond laser induced structure changes in glasses |
| 中文摘要 | 随着激光技术的发展，短脉冲、高功率、短波长逐渐成为激光发展趋势。研究激光与用于制备光学元器件的光学材料的相互作用对提高和拓展激光技术的发展具有重要作用。近年来在研究中发现，飞秒激光与玻璃相互作用后，会在其中诱导点缺陷结构以及产生折射率的永久性改变。这两种效应既有不利的方面，如玻璃的通光性、均匀性降低，影响光传输质量；但同时也提供了新的应用可能，如微光子学器件研制、高密度光存储等。虽然这方面的研究已得到广泛重视，但目前关于飞秒激光引起玻璃微观结构变化的物理机理仍不是很清楚。探索飞秒激光在玻璃中诱导色心和永久性折射率改变的原因，对提高玻璃的性能、发展超强超短脉冲激光系统以及在微型光子学器件中的应用具有重要意义。研究了在宏观破坏之前多组分玻璃和纯石英玻璃的着色现象以及点缺陷形成讨程，尝试解释了飞秒激光与玻璃相互作用引起玻璃微观结构变化的物理机理。飞秒激光与多种光学玻璃相互作用过程中得到了玻璃折射率的改变，在论文中对实验结果进行了简单解释，该方愉咭的工作仍在进行中。1．研究了近红外飞秒激光与多组分玻璃相互作用的着色（暗化）现象，分析了着色原因、影响着色深浅的因素以及着色对激光性能可能产生的影响，解释了着色的物理机理。近红外飞秒激光辐照后，在掺钦的硅酸盐、磷酸盐N21和N31型激光玻璃以及K9玻璃中都观察到了暗化现象。通过分析发现，暗化是由飞秒激光诱导产生的色心引起的。色心主要为空穴型色心。飞秒激光作用下的多光子电离是磷酸盐激光玻璃产生色心的原因，和紫外激光作用下的单光子电离效果相同。色心的平均g因子大小为2.009，结构为色心II、色心III杂化形式。对于硅酸盐激光玻璃而言，飞秒激光作用下的多光子电离和热效应是色心产生的原因。色心包括HCI型色心和SiE'心。在K9玻璃中，生成了非桥氧、空穴心HCZ和硼氧空穴心，非线性电离和空穴捕获是色心形成的原因。在紫外激光作用下，硅酸盐激光玻璃中只产生了HC1型色心，由单光子电离和缺陷结构捕获空穴形成。HC1型色心的形成与玻璃结构中的网络修饰体有关。在两种激光光源辐照后，暗化现象产生的难易顺序为N31＞NZI＞硅酸盐激光玻璃。在紫外激光作用下，暗化饱和顺序为N31＞N21＞硅酸盐激光玻璃。在飞秒激光作用下，磷酸盐激光玻璃比硅酸盐激光玻璃抗辐照能力强，除了与网络结构特性有关外，Nd3+的强吸收峰对激光能量的吸收以及辐射转移也是削弱非线性电离的原因之一。暗化作用引起的紫外及可见光范围的吸收增加，将会削弱Nd3＋对泵浦光能量的吸收，因此会导致激光效率的降低。2．对飞秒激光在纯石英玻璃中诱导点缺陷结构进行了定量研究。分析了点缺陷产生的原因、点缺陷的种类以及玻璃的微观结构对点缺陷结构的影响。对飞秒激光在纯石英玻璃中诱导点缺陷的物理机理进行了分析。飞秒激光辐照后，不同方法制备的石英玻璃性能均发生了变化，通过分析发现主要是由玻璃中诱导产生了点缺陷结构造成的。聚焦的近红外飞秒激光在纯石英玻璃中诱导产生两种SiE'心，分别为Ey'心和E8'心。在宏观破坏前，色心含量随激光功率密度、辐照脉冲数呈线性关系增长。线性关系可以解释为吸收了光子能量的自由电子通过声子将能量传递给晶格，导致晶格温度升高，并引起网络结构的畸变；局域范围内的热传递与沉积的激光能量呈线性关系。通过飞秒激光辐照前后石英玻璃的吸收光谱、电子自旋共振谱、荧光谱分析，提出了超短脉冲激光作用下SiE'心的形成过程，并认为激子自陷是色心形成的主要原因。氧原子脱离原来位置形成氧空位，新形成的氧空位捕获空穴后产生E’心。在ED-C中，C1元素含量较高，因此Si-Cl键可能是E'心产生的重要原因之一。二价硅（Si20）由于光致电离或捕获空穴也可转化为E'心，或者二价硅（Si20）转化为中性氧空位并捕获空穴转化为E'心。石英玻璃中诱导产生的点缺陷结构特性随样品而不同。在含水量较高的ES型石英玻璃中，由于轻基的存在，在石英玻璃中容易形成Si-H键和Si-OH键，处于非平衡状态的价键通过弛豫释放应力，使玻璃网络结构弹性增强。在飞秒激光作用下，ES型石英玻璃抗辐照能力最强。另外还证实了Eδ'，心的形成与石英玻璃中的氯元素没有必然联系。3．对飞秒激光在玻璃中诱导折射率改变进行了初步研究。通过近红外飞秒激光辐照Kg等玻璃的实验研究发现，激光诱导产生的折射率变化随激光功率密度增强而增大。在折射率改变区域伴有暗化现象产生，这与空穴型色心的产生有关。折射率的改变可能与结构致密化有关。 |
| 英文摘要 | Shorter pulse width, higher peak power and shorter wavelength are the trend of the development of laser technology. Understanding the interaction of the laser and optical components is necessary and exigent. In the last few years, it has been found that defects and refractive index change could be induced in glasses by infrared femtosecond laser, which on the one hand is harmful for optical transmission because of the new absorption bands formed in the components and decreased uniformity, but on the other hand, it also provides new applications, such as micro-optical device machining or high-density optical memorizing. Although much effort has been put into the area, the mechanism of femtosecond laser induced structure changes, such as defects generation and refractive index change in glasses, is still ambiguous. We studied the femtosecond laser induced defects in laser glasses and fused silica glasses under the damaged threshold, the possible mechanism for defects generation in glasses was proposed. Refractive index change generated due to femtosecond laser irradiation was also studied, the results were analyzed and conclusions was given in the thesis. The whole results could be divided into three parts and the conclusions listed in the following. 1. Femtosecond laser induced darkening in multi-component laser glasses were studied. The possible reason and the affecting factors were analyzed. Its influence on laser efficiency was explained. The mechanism for femtosecond laser induced darkening was given. Laser-induced darkening was formed in Nd-doped silicate laser glass, N21 and N31 phosphate laser glasses under 800nm femtosecond laser and 266nm nanosecond laser irradiation, which is mainly due to hole-trapped color centers generation in them. Under the femtosecond laser exposure, multi-photon ionization was the main reason for the color center formation in phosphate laser glasses, which produced the same effect as single UV photon-ionization. The average Londe factor g was 2.009, which was due to the hyperstructure of color center II and III. For Nd-doped silicate laser glass, multi-photon ionization and heating attributed to the Si E' center and hole center HCi formation. In K9 glass, nonbridging-oxygen hole centers, hole center HC2 and boron-oxygen hole center were generated, which mainly resulted from optical nonlinear ionization and hole trapping at different sites. Under the nanosecond UV laser irradiation, single-photon ionization and hole trapped at the tetrahedrons with two nonbridging oxygens attributed to the color center HCi formation. Under the same condition of infrared femtosecond laser and UV nanosecond laser irradiation, N31 was most difficult to be darkened, then was N21, and the last one was silicate glass. Higher absorption peak of Nd3+ ions in phosphate laser glass was also one of the reasons for its higher ability to resist color center formation in them than silicate laser glass. Absorption increment in UV and visible bands in the laser glasses would decrease the absorption of Nd + ions from the pump sources, and in the end damp the laser output efficiency. 2. We quantitatively studied the femtosecond laser induced defects in high-purity fused silica glass, analyzed the characteristics and the possible reason for defects formation, and the influences from the microstructure of the network. The mechanism of the femtosecond laser induced defects in fused silica was discussed. Defects were induced in fused silica glasses produced by different methods after femtosecond laser irradiation. Two variants of Si E' center, Ey'(g-2.0006) and Eg' (g=2.0021) were generated. From the results of absorption spectra, electronic spin resonance spectra and fluorescence spectra before and after femtosecond laser irradiation, we anaysised the process of Si E' center formation and proposed that self-trapped exciton was the main reason for its formation. Oxygen atoms displaced from the original site and moved way, a hole trapped at the vacancy resulted in the Si E' center formation. In fused silica ED-C, Si-Cl bond broken might be one of the reason for the Si E' center formation due to the high content of Cl element. Photoionization or hole trapped at divalent silicon would give rise to the Si E§' center formation. Divalent silicon transformed to neutral oxygen vacancy and trapped a hole would also form Si E' center. The characteristics of the defects formation in the fused silica changed with samples. In ES, Si-H and Si-OH bonds could be formed due to the high content of OH. The strained bond could be relaxed and enhanced the flexibility of the network, defects was much difficult to be formed in it. We also found out that Cl was not the necessary factor for the E' center formation. 3. We studied the femtosecond laser induced refractive index change in glasses. Refractive index change induced in various glasses. From the experimental results of femtosecond laser interacting with K9 optical glass, we found out that the change of the refractive index increased with power density. In the irradiated area, darkening and refractive index change generated simultaneously. Darkening was due to hole color centers formed in them. The character of the defects and their production were analyzed. The refractive index change might be due to the densification. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15347]  |
| 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 | 周秦岭. 飞秒激光照射引起玻璃结构变化的研究[D]. 中国科学院上海光学精密机械研究所. 2004. |
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