【作者】 陈彬；

【导师】 余昺鲲； 邱建荣；

【作者基本信息】 上海大学 ， 无线电物理， 2006， 博士

【摘要】 近年来，随着对飞秒激光研究的不断深入，飞秒激光诱导物质微结构引起了越来越多的关注。利用飞秒激光诱导玻璃与晶体微结构可以进一步发掘材料的新性质、新功能。目前，在玻璃与晶体中诱导微结构变化在高密度光存储、光波导、光子晶体、三维显示器件以及三维光器件等的应用已成为世界性的前沿课题。本文从实验上和理论上研究了飞秒激光诱导玻璃中晶体形成与相变。利用飞秒激光在玻璃中诱导晶体形成，研究了晶体形成的机制；并通过飞秒激光诱导出晶体相变，深入研究了相变的规律；理论上对飞秒激光诱导晶体与晶体相变的机制进行了分析，系统研究了飞秒激光诱导玻璃内晶体的形成与晶体相变的成因；探讨了飞秒激光诱导微结构的潜在应用。本文首先利用飞秒激光在玻璃中诱导出偏硼酸钡晶体、铌酸锂晶体、锐钛矿与Ba₂TiO₄晶体，系统地研究了晶体形成的机制。利用飞秒激光对硼酸盐玻璃诱导，在硼酸盐玻璃内形成低温相与高温相偏硼酸钡晶体，详细讨论了飞秒激光诱导下硼酸盐玻璃的微结构变化。实验中首次观察到由于冲击波效应形成晶体的环形分层结构，以及低温相与高温相偏硼酸钡晶体的分布规律，并在晶体形成晶体的同时，观察到由于微爆炸而形成的空洞结构。飞秒激光诱导钛酸盐玻璃形成了锐钛矿晶体和Ba₂TiO₄晶体。利用拉曼光谱在钛酸盐玻璃内分层、分区研究，发现了锐钛矿晶体与Ba₂TiO₄晶体形成与激光参数之间的关系，在激光焦点区域实现了锐钛矿晶体与Ba₂TiO₄晶体的分层共存。利用飞秒激光在铌酸盐玻璃内诱导出铌酸锂晶体，控制飞秒激光的参数，在玻璃内部的任意空间内诱导出光学中的“硅材料”铌酸锂晶体。其次，利用飞秒激光诱导偏硼酸钡晶体、铌酸锂晶体等晶体相变。飞秒激光诱导偏硼酸钡晶体，在高温相偏硼酸钡晶体内部诱导形成了低温相偏硼酸钡晶体，初步分析了相变不完全的原因。在未经抛光的铌酸锂晶体表面诱导出光栅结构，并形成了其它晶相。本文以硼酸盐玻璃为例，对飞秒激光诱导晶体与晶体相变的机制进行了理论上的探讨，重点研究了光电离与雪崩电离、等离子体的自由载流子吸收、微爆炸、动态平衡、基团重组、热扩散等，系统分析了飞秒激光诱导玻璃内晶体的形成与晶体相变的成因。飞秒激光辐照硼酸盐玻璃的初始能量的沉积是由于多光子吸收与雪崩电离的结果，等离子体密度很高时就能在局部区域强烈地吸收激光能量，从而产生高密度超热高压等离子体，导致微爆炸；由此长时间的辐照会在玻璃内部形成一个空洞结构，外围的材料则会形成一个较大的温度梯度；高温高压下，玻璃中的化学键断裂，组成玻璃的基团开始重组；激光辐照结束，这一区域的材料的快速不均匀冷却使得硼酸盐玻璃上形成了高温相与低温相两种结构类型的偏硼酸钡晶体。此外，飞秒激光的高重复率也是形成晶体的关键。飞秒激光技术能使固体材料中微结构基元重新组合，改变其性能，开拓了同质异构形成规律的新途径，也是研究晶体结构与性能的新方法。本文从玻璃与晶体的结构基元出发，系统研究了硼氧六元环、钛氧八面体、铌氧八面体等微结构基团在飞秒激光作用下的演变，分析了玻璃与晶体微结构特征，为指导功能晶体生长实践和促进实际晶体生长理论发展提供了科学依据。同时利用飞秒激光诱导玻璃中晶体形成与相变可以将各种不同功能的光子微结构集成在玻璃与晶体内部，为探索和研究微光学器件的发展起到了重要的作用，为光学集成技术的发展提供了一种新思路。更多还原

【Abstract】 Recently, with the development of the scientific research, much attention has been paid on the microstructures induced by femtosecond laser. Femtosecond laser can be used to induce microstructures in glass and crystals to find new properties and functions of the optical materials, thus the applications of the microstructural changes in glass and crystals induced by femtosecond laser have been a worldwide hot topic in high dense optical storage, optical waveguide, photonic crystals, three-dimensional display devices, three- dimensional optical devices and so on.In this paper, crystals generation in transparent glass and crystals phase transitions induced by femtosecond laser are analyzed experimentally and theoretically.These studies begin with the research about the generation of barium metaborate crystals, lithium niobate crystals, anatase crystals and Ba₂TiO₄ crystals induced by femtosecond laser, the mechanism of which is studied systematically.High temperature phase barium metaborate crystals are generated in the borate glass irradiated by femtosecond laser. Accordingly, the behavior of the transformation from borate glass is studied, and the microstructural characters of the irradiated area in the borate glass after femtosecond laser irradiation are discussed. Stratified spherical structures about low temperature phase barium metaborate crystals due to blast wave effect is detected the first time, and a void is observed in the borate glass as a consequence of microexplosion accompanied by the generation of crystals.Anatase crystals and Ba₂TiO₄ crystals are generated in different femtosecond laser irradiation conditions. Raman spectroscopy is employed to analyze the titanate glass in depth and radial direction. Consequently, the relations between the growth of anatase and Ba₂TiO₄ crystals and irradiation time and other irradiation conditions are obtained, and anatase and Ba₂TiO₄ crystals coexistence can be obtained in the focal area.Microstructural character of the niobate glass is also investigated, and lithium niobate crystals are produced in three-dimensional space by controlling femtosecond laser power and irradiation time.Secondly, crystals phase transition of barium metaborate crystals and lithium niobate crystals is induced by femtosecond laser.Crystals phase transition is induced in barium metaborate crystals, and low temperature phase barium metaborate crystals are produced in high temperature phase barium metaborate crystals via femtosecond laser induction. For the lithium niobate crystals, other crystal phases are also generated by femtosecond laser irradiating the surface of the lithium niobate crystals.Finally, the mechanism of the crystals formation and crystal phase transition induced by femtosecond laser is studied by taking the borate glass as an example. The photo ionization and avalanche ionization, free carrier-absorption, microexplosion, dynamic equilibrium, group reunion and heat diffusion are emphasized in this study; accordingly, the origin of the crystals formation and phase transition is analyzed systematically. When femtosecond laser irradiates the glass, the laser energy deposit begins due to multiphoton and avalanche ionization. Thus the laser energy is absorbed intensely in local area when the density of the plasma is high enough. And microexplosion takes place when the plasma is extremely high in density, temperature and pressure. Therefore, a void in borate glass can be generated during long time femtosecond laser irradiation, and high temperature gradient is formed the material nearby. So bonds breaking and groups’ reunion occur in high temperature and pressure conditions. When the laser is turned off, high temperature phase and low temperature phase barium metaborate crystals are generated in different place as a result of the nonuniformity of the cooling process in the borate glass. Moreover, another key condition to form crystals is the high repetition rate of the femtosecond laser.Recombination of the microstructural motif in solid material is achieved by using femtosecond laser technique, and new performance of the material is obtained in this paper. Therefore, a new approach is offered to discover the rule of the formation of tautomerism, and to study the structure and character of glass and crystals. Based on the structure motif of the glass and crystals, the transformation of B₃O₆ rings, NbO₆ octahedra, TiO₆ octahedra and other microstructural units are studied, and the microstructural character of glass and crystals are analyzed experimentally and theoretically in this paper, which can guide the practice and advance the theory of synthetic crystal growth.Also, photonic microstructures integrated in glass and crystals induced by femtosecond laser are of vital importance in research and fabrication of the photonic devices. Hence, the way to form crystals in glass substrate by femtosecond laser provides a brand new method in integrated optics technique.更多还原