【作者】 朱利；

【导师】 崔一平；

【作者基本信息】 东南大学 ， 物理电子学， 2006， 博士

【摘要】 非线性光学材料在高速光通信、光信息处理、高密度光存储等领域得到了广泛的应用。有机材料因其非线性系数大、响应速度快、损伤阈值高、介电常数低、可加工性好而日益成为非线性光学材料研究的热点。但是,大的非线性光学系数往往伴随着长的吸收波长,导致透明范围变窄。这就是所谓“非线性-透光性矛盾”。本文首先综述了优化“非线性-透光性矛盾”的有机材料的几种研究策略,即在发色团设计层面的选择特殊的共轭桥、寻求给、受体强度的最佳组合和设计双(多)重电荷转移分子以及在晶体设计层面的构建有机包结络合物。本文研究一种新型有机包结络合物L-苹果酸脲,该材料为手性分子L-苹果酸与尿素分子以氢键结合形成的一种高度非中心对称的有机晶体,很好地平衡了“非线性-透光性矛盾”。本文采用粉末倍频法研究了ULMA的二阶非线性光学效应,实验结果表明ULMA的非线性光学系数为KDP的1.57倍(1064 nm基频波),并且其激光损伤阈值接近KDP的2倍;首次对ULMA进行了宽带倍频研究,发现其在900～1300 nm范围均有明显的倍频效应,得到了此范围的非线性系数的色散曲线。采用HRS法测量了ULMA的一阶超极化率,实验结果显示其β值与底物尿素相当,即保持了尿素的良好的非线性光学性质。对ULMA晶体进行了相位匹配研究,数值模拟了第I类和第II类相位匹配曲线,为今后ULMA相位匹配的实验研究打下了基础。根据ULMA的结构特点采用手性非线性极化理论中的螺旋单电子模型分析了ULMA的一阶超极化率的色散关系,计算结果与实验结果吻合良好,证明了模型和参数选择的正确性。讨论了微观参量对一阶超极化率的影响,分析和计算表明阻尼系数Γ表征了材料的非线性转换效率;固有频率ω0、螺距ξ和回旋半径ρ共同影响着β的峰值位置、形状和大小。β的峰值频率正比于材料的固有频率ω0,并小于固有频率,其对固有频率的偏离则取决于ρ/ξ。因此,在设计兼备大的二阶非线性光学系数与良好光学透过率的有机复合物材料的过程中,选择不同的手性分子作为有机包结络合物主体,再辅以分子修饰等手段,可以在较大范围内调节ρ/ξ的比值,以获得所需要的非线性光学响应。首次制备了ULMA晶体薄膜,该薄膜保持了晶体的良好的非线性光学性质。运用热分析手段研究了ULMA薄膜形成机理,实验结果表明ULMA蒸发温度低于底物尿素和苹果酸的分解温度,因此采用热蒸发法制备ULMA晶体薄膜成为一种可行的方法。更多还原

【Abstract】 Nonlinear optical materials have been widely used in applications such as high-speed optical communication, optical signal processing, and high-density data storage. The research on organic nonlinear optical materials is attracting more and more attention because organic-based materials have larger nonlinear coefficients, faster response speed, higher damage thresholds, lower relative permittivity, and easier processability than those of inorganic materials. However, the larger nonlinear optical coefficients are always accompanied by longer maximum absorption wavelength. This correlation is called nonlinearity-transparency tradeoff. In this dissertation, the strategies of balancing the nonlinearity-transparency tradeoff are reviewed, including the utilization of special conjugated bridge, the optimal combination of donor-acceptor’s strength, and the introduction of dual (mutiple) charge transfers in the design of chromophores and the construction of organic inclusion complex.The study on a new organic inclusion complex - urea L-malic acid (ULMA) - is described in this dissertation. ULMA crystal is constructed with L-malic acid held together by hydrogen bonds (O-H…O) with urea. It is a type of organic crystal able to optimize nonlinearity-transparency tradeoff.The Kurtz powder method was used to study the second order nonlinear optical properties of ULMA. Experiments showed that the nonlinear optical coefficient and laser damage threshold of ULMA were 1.57 times and 2 times, respectively, of those of KDP (@1064 nm). The broad band second harmonic generation (SHG) of ULMA was studied for the first time and the nonlinear coefficient dispersion relation was achieved in the range of 900~1300 nm. The first order hyperpolarizability of ULMA is within the same magnitude of that of urea measured by the Hyper-Rayleigh scattering method. Phase-matching of ULMA was studied. Both type I and type II phase-matching angles were numerically simulated. The results provided the foundation of phase-matching experimental study.The model of a single electron along a helical path for chiral molecular nonlinear polarization theory was chose to analyze the first order hyperpolarizabilities dispersion relation of ULMA based on its structure characteristics. Numerical simulation results were in agreement with the experiment data. The influences of microscopic parameter to the first order hyperpolarizability are discussed. Damping coefficient is a token of nonlinear conversion efficiency. The inherent frequencyω0, pitchξ, and radiusρare involved in the position, figure, and magnitude of the peak ofβ, respectively. The peak frequency ofβis proportional toω0 and less thanω0. The departure toω0 was determined byρ/ξ. Therefore, selecting different chiral molecular as host to adjustρ/ξcan achieve appropriate nonlinear optical response.ULMA crystalline film was prepared for the first time. Furthermore, the film keeps the nonlinear更多还原