基于SHG观察的飞秒激光操控玻璃三维析晶及其二阶非线性调控

The optical nonlinear glass was regarded as one kind of important candidate materials and was taken much attention due to its easy fabrication and interegation for all-optical devices, especially the existence of nano-crystals in glasses will induce an enhancement of optical non-linearity,this endues glasses great potential application and attacts much attention in achieving all-optical network optical switching, etc. Indeed, the presence of nano-sized crystals in an otherwise transparent matrix ensures material properties which are quite different from those of the bulk matrix materials. It is strongly dependent on the size, shape, distribution and orientation of the crystalline structure. So it is still under resolved for mastering the nonlienar optical properties according to the crystalline structure. As a result, the new approach, such as ultra-fast laser irradiation, has been proposed as an efficient means to realize the controllable 3D modification in transparent materials. This might become a guide for design and fabrication of nouveal nonlinear optical materials with multifunction. The first of this program is to investigate the variations of nano-crystals embeded SiO2-based glasses under femtosecond laser irradiation which will induce the change of glass structures. The second approach is to realize the controllable 3D crystallization of nano-crystals by adjusting femtosecond laser parameters. We will investigate the variations (size, distribution and orientation) of nano-crystals (BaTiO3, Ba2TiSi2O8, Ba2TiGe2O8) embeded SiO2-based glasses like (BaO-TiO2-(Si,Ge)O2 glass series) by changing femtosecond laser irradiation parameters (polarization, energy, frequency, etc), which will induce the change of crystalline structures. With analyzing the behavior of those nano-crystals, the mechanism of their precipitation and orientation based on the interaction between femtosecond laser and materials, thermodynamics of crystallization in glass, the formaiton and variation of crystalline structure related to glass optical properties will be clarified to get an efficient method to improve the controllable crystallization and non-linear property in SiO2-based glasses. After rationalizing the relationship among intense light fields, nano-stucture in glasses and non-linear properties of bulk glasses, the results of this objective will provide better knowledge in theory and technology for designing and preparing high-performance non-linear glasses for photonic devices like optical switching, which offers the opportunity to manufacture very promising new nonlinear materials for nano-devices and optical elements by manipulating the nano-structural properties of the composite media.

非线性光学玻璃由于易加工与集成等优点成为全光网络器件低成本制备的重要候选材料而倍受关注，尤其含微/纳米粒子玻璃产生非线性增强更是热点，但如何利用微/纳米粒子特性调控玻璃非线性来满足器件使用要求一直未能深入探讨与解决。利用飞秒激光脉冲短、能量高等优点可以操控材料三维空间结构构筑新型多功能光学材料。本项目根据基体玻璃析晶特点，通过飞秒激光辐照操控玻璃三维析晶，改变激光偏振方向、能量及频率等调控粒子大小、形貌、分布、取向等，结合强光与物质之间的相互作用机理以及玻璃成核-析晶等热力学、动力学理论，探讨玻璃中晶粒形成及变化机理，及其对玻璃结构和性能的影响，分析飞秒激光外场诱导-微/纳米粒子变化-玻璃微结构形成-非线性光学性能之间的关系，阐明含微/纳米粒子玻璃二阶非线性增强机理。在此基础上，通过飞秒激光操控三维析晶有效调控玻璃非线性光学性能，制备出高性能非线性光学玻璃并应用于全光开关等光子器件中。

非线性光学玻璃由于制备工艺简单、成本低廉、高透过率、物化性能温度等优点受到越来越多的关注。由于玻璃块体内非线性晶粒微结构的排列可使玻璃显示出各向异性的物理性能。因此，利用外场诱导(热场或飞秒激光强光场)在玻璃内控制析出晶体的晶相、分布、大小以及取向等实现非线性光学性能可控，对于设计及制造新型多功能非线性光学材料有十分重要的指导意义。. 利用传统的高温熔融-淬冷法，选择合适的玻璃组分，制备出了物化性能稳定、紫外-可见波段透过率较高的BaO-TiO2-(Si,Ge)O2玻璃。两者的熔融温度分别是1550 ℃和1250 ℃。分析了不同升温速率下得到的DSC曲线，利用固相反应动力学方程和JMAK方程，得到40BaO-20TiO2-40GeO2玻璃的析晶活化能分别为387 KJ/mol和369 KJ/mol，Avrami指数接近于3。这一结果表明在等温和非等温条件下导出的公式计算的E值差异不大，该组分玻璃的晶化过程为体积晶化。在BaO-TiO2-GeO2玻璃体系中，随着二氧化钛含量的增加，玻璃的吸收系数增加，紫外吸收截止边红移，玻璃转变温度有所增加，T值有所下降。测试结果表明Ge4+离子不随二氧化钛的加入发生配位数的变化，始终以[GeO4]四面体的形式存在于玻璃网络中。Ti4+离子存在[TiO4]和[TiO6]两种不同的微结构单元，并且随着玻璃中二氧化钛含量的增加，部分[TiO4]向[TiO6]转变。. 利用玻璃在外场作用下可以诱导出不同的微观结构，从而制备出不同性能的光学玻璃材料。通过500 kHz的高重复频率飞秒激光成功地在40BaO-20TiO2-40SiO2玻璃内部诱导析出了非线性光学晶体。分析了不同参数的飞秒激光辐照后，在30BaO-15TiO2-55GeO2玻璃内部留下的痕迹。结果表明，写入线的结构受激光的重复频率和脉冲能量的影响较大，而对激光扫描速度的变化不明显。在低重复频率如200 kHz及低脉冲能量如5.0 J以下，可以在玻璃内部得到光滑的亮线，从而在玻璃体内实现激光直写光波导。非线性光学玻璃良好的光学性能等将在光子通信器件，如光开关等，具有很好的应用前景。

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