| 题名 | 超短激光脉冲诱导ZnO纳米结构的生长及其特性研究 |
| 作者 | 郭晓东 |
| 学位类别 | 博士 |
| 答辩日期 | 2010 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 李儒新 |
| 关键词 | 飞秒激光 微纳结构 水热生长 高次谐波 |
| 其他题名 | Ultrashort laser pulses induced ZnO nanostructures and its properties |
| 中文摘要 | 由于飞秒激光具有超短的脉冲宽度和极高的脉冲峰值功率，在与材料的相互作用过程中主要是基于多光子电离过程和碰撞电离过程，因此飞秒激光有着长脉冲激光无可比拟的优点。近年来，飞秒激光在材料上写入功能化的微纳结构得到了越来越多的关注。常见的周期微结构加工方法有飞秒激光直写法和多束激光干涉法。最近的研究发现，单束飞秒激光借助超显微技术即可诱导可控周期性的微结构。进一步深入研究飞秒激光诱导的自组织周期性微纳结构不仅在探索微纳加工方面具有重要意义，还促进了强场激光物理、等离子体物理、非线性光学和材料学等学科的发展。 本论文对飞秒激光与氧化锌晶体以及二氧化碳分子相互作用进行了理论与实验研究工作。研究的内容主要包括飞秒激光诱导氧化锌纳米结构的相干耦合连接形成纳米光栅、飞秒激光诱导选择性可控生长氧化锌三维纳米结构、可控生长氧化锌纳米结构的润湿性和光催化特性、利用高次谐波研究取向分子中的电离效应和复合干涉效应等几个领域。本文的工作以及所取得的主要创新性成果有以下几个方面: 1.利用飞秒激光脉冲在氧化锌晶体表面诱导出规则的纳米结构。对比了不同飞秒激光系统诱导氧化锌纳米结构，分析了在不同烧蚀气氛对形成纳米结构的影响。实现了飞秒激光脉冲辐照氧化锌晶体表面诱导纳米条纹的相干连接，发现逐渐减小两次激光扫描区域的间距时，两次独立形成的纳米条纹可以相干的连接起来，形成更长的纳米光栅。这样就解决了以前诱导光栅尺寸由激光聚集光斑大小限制的问题。利用Raman线扫描技术分析了相干连接的条纹，并对相关的物理机制做了讨论。搭建了泵浦-探针系统，用于在飞秒激光微加工过程中实时的观测表面反射率的变化，为研究飞秒激光诱导纳米条纹的形成机理提供了实验依据。 2.利用飞秒激光直写与水热生长方法相结合，在GaN/LiAlO2样品表面成功生长出选择性可控的三维氧化锌纳米结构。通过控制飞秒激光脉冲的参数，包括功率密度，辐照时间，扫描速度等参数可以控制生长纳米结构的尺寸，位置和结构。通过改变水热生长的条件，可以对纳米结构的形貌进一步控制。用扫描电镜、透射电镜、能谱、选区电子衍射以及荧光谱等对生长的纳米结构进行了表征。对比了激光辐照区域和未辐照区域，晶体生长的形貌区别。水热生长过程中分析了不同时间生长的纳米结构，对纳米结构的形成机理做了系统的研究。 3.在实验上给出了通过激光直写方法诱导氧化锌纳米结构的润湿性以及光催化特性的结果。分析了选择性可控生长对纳米结构润湿性的影响，对比了纳米材料生长前后润湿性的变化，并给出了材料的实时接触角的数值，结果表明通过本方法诱导的纳米结构可以改变纳米材料的润湿性，这样对进一步拓展纳米结构的应用提供了一种新的方法。通过实时的观测纳米氧化锌分解罗丹明B的催化实验，分析了本方法生长的氧化锌纳米结构的光催化特性。 4.在飞秒激光与气体靶相互作用的实验中，我们利用高次谐波研究了自由场中分子的取向动力学过程。研究了二氧化碳分子谐波产生和取向度对取向脉冲强度的依赖关系。在比较低的脉冲强度下，谐波强度随着脉冲强度的增加而单调上升，直到电离导致的折射率梯度和中性分子消耗达到阈值。理论计算和实验结果表明二氧化碳分子最佳的功率密度在8.95×1013W/cm2，这个数值与分子的电离势有关。还研究了二氧化碳分子角分布与谐波级次以及驱动脉冲强度的关系，分析了分子间的量子干涉和激光强度的关系。建立了激光场复合干涉模型来解释谐波产生的分子取向调制翻转，通过改变激光强度可以操纵在复合过程中的双中心干涉。 飞秒激光与半导体材料、分子气体相互作用这一研究领域将超快光学、材料科学以及激光光谱学结合起来，是一个多学科交叉的领域。开展这方面的研究一方面可以促进新的有源或无源光子学器件的发展，另一方面可以利用飞秒激光的特性发掘材料的新功能，发现更多在普通条件下无法观察到的新奇的物理现象，促进非线性光学以及相关研究的发展。 |
| 英文摘要 | Because of its ultrashort pulse and ultrahigh peak power, nonlinear optical effects are dominant in the process of femtosecond laser interaction with materials. This is based on the multiphoton ionization and the avalanche ionization, so this process is strictly limited by the threshold intensity of incident laser. Thus, femtosecond laser could space-selectively induce various functional microstructures. Recently, much attention has been paid on the functional micro/nanostructures induced by femtosecond laser pulses. Generally, the fabrication of periodic microstructures using a femtosecond laser pulse can be used either by the three-dimensional direct-writing method or by the holographic interference method. Recently，with the help of super-microscopy technologies, researchers found that a single femtosecond laser beam could also induce controllable self-organized nanostructures. Further studies concerning the laser direct writing induced microstructures are important not only for exploring the micromaching method, but also for the developments of high-field laser physics, plasma physics, non-linear optics and material science. In this dissertation, part of theoretical and experimental studies on the interaction of ultrashort ultra-intense laser pulses with solid and gas targets are presented. The main contents in this dissertation include coherent linking of ZnO nanogratings induced by femtosecond laser pulses, femtosecond laser controlled selectively growth of ZnO nanostructures, synthesis of ZnO nanoflowers and their wettabilities and photocatalytic properties, ionization effects on field-free molecular alignment observed with high-order harmonic generation，laser-field-related recombination interference in HHG from CO2 molecules. The main research results are summarized as follows: 1.Femotsoecond laser was employed to induce regular nanostructures on the surface of ZnO crystal. The deference of ZnO nanostructures induced by different femtosecond laser systems was presented; the influence of the ablation atmosphere on the nanostructure was analysised. By adjusting the distance between two laser scanning zones, the periodic nano-ripples induced by two separated laser writing processes can be coherently linked and the ZnO nanograting with much longer grooves is therefore produced. The length limitation of this kind of nanograting previously set by the laser focus size is thus overcome. The micro-Raman mapping technique is used to evaluate the quality of coherent linking, and the underlying physics is discussed. We constructed a pump-probe system to detect the in-situ surface albedo, and provided experimential base for further study the mechanism of laser induced nanoripples. 2. A method combing laser direct writing (LDW) and hydrothermal growth was developed for the synthesis of micrometer-sized three-dimensional (3D) ZnO nanostructures. Controlling parameters of the nanostructures including not only hydrothermally conditions such as reaction time, precursor concentration and reaction temperature, but also laser ablation parameters such as pulse energy, irradiated time, focus conditions, different morphologies of ZnO nanostructures were synthesized. Characterization of the flowerlike nanostructures was performed by field-emission scanning electron microscopes (FESEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SEAD), and micro-photoluminescence spectroscopy (μ-PL). The analysis of various possible mechanisms that might illustrate the flowerlike nanostructures formation is discussed. 3.By combing laser direct writing and hydrothermal growth, we demonstrate the growth of three-dimensional (3D) flowerlike ZnO nanostructures from aqueous solution. Our approach offers synthetic flexibility in controlling film architecture, surface topography, coating texture and crystallite size. The time-dependent contact angle (CA) was studied in the as-grown samples. In addition, superior photocatalystic propertiey of the flowerlike ZnO nanostructures in the degradation of Rhodamine B has been demonstrated. The influence factors and formation mechanism of the flowerlike ZnO nanostructures were also analyzed and discussed. 4.High-order harmonic generation (HHG) is demonstrated to provide a sensitive way for studying the dynamic process in the field-free molecular alignment. The dependence of the harmonic yield and the degree of alignment on the intensity of aligning pulse is observed in impulsively aligned CO2 molecules. A good agreement is found between the experimental and calculated results. At low pump intensities, the harmonic yield increases monotonously until the ionization induced refractive index gradient and neutral molecule depletion are significant. The results show that the optimum intensity is around 8.95×1013W/cm2, which is related to the molecular ionization potential. The angular distribution is found to be sensitive to both the harmonic order and the intensity of the driving laser pulse for HHG. The roles of intramolecular quantum interference and the laser intensity are clarified. A laser-field-related recombination interference model is proposed to explain the modulation inversion of harmonic yield with respect to the molecular alignment. We conclude that the two-center interference in the recombination process can be manipulated by changing the laser intensity. Interaction of ultrashort laser pulses with semiconductors and molecule gas is a multidisciplinary study which connected ultrafast optics, materials science and laser spectroscopy. Researches in this area will promote the development of active or passive components; on the other hand, using femtosecond laser to realize the new function of material and find more interesting physical phenomena will also promote the development of non-linear optics and related fields. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15646]  |
| 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 | 郭晓东. 超短激光脉冲诱导ZnO纳米结构的生长及其特性研究[D]. 中国科学院上海光学精密机械研究所. 2010. |
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