纳米材料的非线性光学效应研究

Nanomaterials have been extensively studied, and showed extraordinary optical properties. Here we will focus on the nanomaterials of ZnO, CdS, Au, and Ag and the nonlinear optical effects of second harmonic generation (SHG)and Raman scattering. The excellent properties of nanomaterials, such as low loss, smooth surface and regular geometry, will be taken into account for nonlinear optics. With matching size between the nanomaterials and the field distribution of surface plasmon polaritons (SPPs), the integration of nanomaterials and SPPs can constitute nano-optical devices, serving for miniaturized photonic circuits. Moreover, the enhancement of near-field intensity, originated from artificial structures, will result in strong nonlinear optical signals, which is of importance for practical applications, e.g. in metamaterials and photovoltaic solar cells. We will combine theory with experiment in our research work. Theoretical work will be employed further by means of simulation softwares based on finite-element method, and finite-difference time-domain method to get the near-field behavior of nanomaterials. The bottom-up and top-down approaches will be adopted to the nanomaterial-involved structures. The novel optical phenomena as well as the mechanism are expected to be revealed by the experimental measurements of SHG/Raman microscopy, time-resolved spectroscopy, scanning near-field optical microscopy, and k-space spectroscopy.

对纳米材料光学性质的研究有助于纳米光学器件的实现，具有非线性光学效应的纳米材料无疑将是纳米尺度下非线性光学器件的载体。我们拟以ZnO、CdS、Au、Ag纳米材料为对象深入、系统地研究其二次谐波产生、拉曼散射等非线性光学效应。将纳米材料的优异性能引进非线性光学领域，如低的光学损耗、单个纳米材料的光学腔结构等。进一步引入极化激元，如表面等离激元，结合纳米材料，致力于集成光路中小型化非线性光子器件的研制。考虑人工周期微纳结构带来的光学近场增强等效应，结合人工特异材料、太阳能电池等应用领域开展纳米材料的非线性光学效应的研究。理论结合实验，理论上借助于有限元和有限差分方法深入研究这一系统。实验上采用化学合成与气相沉积法制备纳米材料，利用EBL、FIB、SEM、AFM等微/纳加工手段制备与表征纳米结构，采用非线性光学显微镜、近场光学显微镜、倒空间光谱测量系统以及时间分辨测量系统进行光学性能测量。

以提升非线性光学效应的效率为目标，重点研究了光频转换以及拉曼散射等非线性效应。合成制备ZnO、LiNbO3等微/纳米线，观测回音壁等腔谐振模式的增强性能。通过严格位相匹配以及准位相匹配的结构设计，提高光学超晶格结构材料的频率转换效率，并演示了非线性全息成像、克服衍射极限成像、光束整形、时间反演对称等应用。引入表面等离激元，通过结构设计、崭新物理机制、微纳制备工艺、低损耗全介质材料等进一步增强非线性效应。理论上，通过数值计算编程以及模拟计算，分析、推导光学超晶格中的非线性频率转换过程，周期结构的光子能带结构，光学结构的模式传播特性，提取新颖物理效应，并指导实验工作。实验上，采用从上至下法与从下至上法制备一维、二维及三维人工微纳结构材料，开展二次谐波产生、表面增强拉曼散射等光学测量。