【作者】 何漩；

【导师】 刘启明； POUMELLEC Bertrand；

【作者基本信息】 武汉理工大学 ， 材料学， 2013， 博士

【摘要】 在过去几十年中,非线性光学材料由于在光通信方面的应用引起了研究者极大的兴趣。其中,非线性光学玻璃由于其制备工序简易、成本低廉等优点受到越来越多的关注。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。基于这一原理,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。首先,本文在SrO-TiO2-SiO2玻璃中采取传统的热场处理进行诱导析晶,通过Maker条纹法及X射线衍射等方法来分析玻璃中Sr2TiSi208晶体的析出行为,并研究其二阶非线性光学性能。研究表明,经过热处理后,玻璃表面易析出具有择优取向的非线性Sr2TiSi2O8晶体,其极轴c轴与样品表面垂直。随着热处理温度的升高或处理时间延长,Maker条纹测试中在玻璃表面垂直方向得到二次谐波产生信号,表明玻璃由表面定向析晶开始向内部发展,且变为玻璃内部自由取向的体析晶。热处理析晶虽然可以得到微纳米定向析晶,但是由于其可控性差且耗时长等缺点,难以实现空间析晶可控,因此我们提出另一种处理方法,即飞秒激光辐射诱导法。由于在时间和空间上可对飞秒激光的能量累积进行有效控制,飞秒激光微加工透明材料当前受到研究者越来越多的关注。基于这种原理,利用飞秒激光诱导处理的精确性,在玻璃内部控制析出晶体的晶相、大小、形状、分布及其取向,诱导产生特殊的线性和非线性光学特性,对于制造新型多功能复合材料以及激光应用技术等研究领域具有十分重要的指导意义。因此,本论文介绍了高重复频率(如300kHz)的飞秒激光在硅酸盐玻璃三维空间内部成功诱导析出具有取向的铌酸锂(LiNbO3)晶体以及锶钛硅(Sr2TiSi2O8)晶体。在Li2O-Nb2O5-SiO2玻璃中,可以通过调节脉冲能量以及使飞秒激光的偏振方向与激光扫描方向平行在玻璃内部的激光线中得到微米／纳米级的非线性晶体颗粒。通过电子背散射衍射测试结果发现,在低脉冲能量且偏振方向与激光移动方向平行时,可得朝向与激光移动方向平行的定向非线性纳米晶。倍频测试结果显示,在宏观激光线中非线性纳米晶具有整体的择优取向性。另外,为了更好的研究纳米晶在激光线中的取向性,我们进行了一系列相干纳米晶的倍频测试,发现写入方向相反的激光线中非线性晶体的极轴取向性。通过X射线能谱分析及核子微探针等方法对激光线进行化学分析,并借助静态模式以及移动过程中辐照区域的温度场及化学势梯度分布情况,来分析晶体析出及定向生长的机理。在SrO-TiO2-SiO2玻璃系统中,我们分别在化学计量组分及非化学计量组分的玻璃样品中进行激光辐射诱导。前者中,发现改变激光辐射条件不仅可以得到晶体大小、分布的可控析出,同时也可控制玻璃中析出的晶相。倍频测试结果显示该样品激光线中非线性晶体(大尺寸或微／纳米晶)的极轴大致与激光移动方向平行。而在非化学剂量组分玻璃中,激光诱导后玻璃中可获得纯Sr2TiSi2O8晶体。同时采用电子背散射衍射测试方法,讨论了各种激光参数如写入方向和激光偏振对非对称性写入及定向析晶的影响,研究了玻璃中的超快不对称性写入及定向析晶现象。探讨了激光与材料的相互作用过程,为控制激光写入提供了有利的理论依据。研究表明,这种不对称性写入主要是由超快激光固有的脉冲前端倾斜的存在而造成。同时,这种脉冲前端倾斜受飞秒激光的偏振方向影响而产生不同的各向异性的光敏性,从而导致晶体析出及生长过程中晶体的取向性差异。更多还原

【Abstract】 In the past few years, nonlinear optical materials have attracted much attention due to their application in optical telecommunications. Nonlinear optical glass-related materials have been widely studied according to their advantages. Glass ceramics having an aligned microstructure would exhibit anisotropy of physical properties. This dissertation mainly contributes to the control of micro/nano-crystallization in silicate glass in crystalline phase, distribution, size and orientation under additional field, particularly by femtosecond irradiation, to master the nonlinear optical properties of glass further. This work is significant for the design and production of novel nonlinear optical material with multi-function in future.In this thesis, thermal field was used to induce crystals in SrO-TiO2-SiO2glass. The crystallization behavior of glasses in different heat-treated condition and their second-order nonlinear optical properties have been analyzed by Maker fringes method and X-ray diffraction measurement, respectively. It showed that the oriented crystallization of nonlinear Sr2TiSi2O8crystals can be obtained in the surface layer by heat treatment. The polar axis of oriented crystals was perpendicular to the sample surface. Moreover, by applying higher temperature or prolonging the time duration of heat treatment, the maximum intensity of second harmonic generation shifting toward0°is likely due to the presence of randomly distributed crystals in glass and surface crystallization turns to be volume at this moment.However, since it is hard to control crystallization by heat treatment and time-consuming, femtosecond laser irradiation was proposed to realize the control of crystallization in glass owing to the accessible control of energy deposition in time and in space. It opens fantastic opportunities to manufacture novel multifunctional materials by manipulating the crystallization of nonlinear crystals embedded in glasses. Therefore, we achieved to precipitate preferential oriented LiNbO3and Sr2TiSiiO8crystals in glass with femtosecond laser irradiation at high repetition rate (typ.300kHz). In Li2O-Nb2O5-SiO2glass, we obtained micro-/nano-crystals in glass sample by varying pulse energy and polarization direction. Specifically, when applying low pulse energy and polarization parallel to laser writing direction, the oriented nano-crystallization has been obtained as shown by EBSD (Electron back-scattered diffraction). Second harmonic (SH) microscopy measurement illustrated preferred orientation of crystallization in laser lines. In order to understand the exact orientation of crystals with respect to the writing direction, a series of coherent SH measurement has been achieved in pairs of laser lines written in opposite orientation. EDS (Energy Dispersive Spectrometer) and nuclear micro-probe has been used to realize the chemical analysis in laser lines. The mechanism of oriented crystallization was discussed both in static mode and in dynamic mode through illustrating the distribution of different gradients.In SrO-TiO2-SiO2system, laser irradiation was applied both in stoichiometric and non-stoichiometric glasses. In the former case, not only the size and distribution can be controlled by varying laser parameters, but also the crystalline phase can be chosen in samples. SH microscopy measurement was used to characterize the nonlinear properties of glass and it implied that the polar axis of crystals is always along the writing direction. In non-stoichiometric glass, only pure Sr2TiSi2O8crystals were obtained. The asymmetric writing involving oriented crystallization has been studied by varying polarization and writing orientation. The orientational dependent is likely due to the combined action of oblique pulse front tilt affected by the polarization orientation plane leading to different anisotropic photosensitivity and its aftereffects to induce asymmetric distribution of thermal and chemical gradients.更多还原