Search for Organic Nonlinear Optical Materisls and Estimation of Figure of Merit

1. 为了测量有机分子的二阶超极化率，提出了一种紧凑的、改进的电场诱导二次谐波产生方法。该方法还可以消除在单元窗处产生的二次谐波与待测二次谐波之间不可避免的干扰对前一方法的影响。新的理论表达式被导出来描述与这种新结构相关的宏观非线性极化。它已经应用于有机分子，p-NA和MNA，其超聚性已经已知，并应用于未知的MBA-NP， PNP和DAN。用P-P-P法和CNDO/S法测量的结果与理论计算吻合较好。本文认为，由于分子排列良好的有机晶体的相干长度太短，用粉末法评价晶体二阶非线性的优值不宜用于有机晶体。只有分子几乎相互平行的晶体才能超过LN的d33，它被用于波导器件形式的半导体激光器的有效倍频器。为了寻求易于使用的有机材料，需要一种新的或改进的方法来代替粉末法。对于超极化率足够大的片状晶体，提出了两种方法来估计其层值。一种是用光谱仪或椭偏仪测量具有光学等级的晶体的折射率，另一种是用x射线法分析和了解具有光学劣化等级的晶体中的分子取向。从MBA-NP和DAN的测量结果来看，这两个程序都是互补的。

1. As compact and modified method of electric-field induced second-harmonic generation has been developed for measuring the secon-order hyperpolarizability of organic moleucules. The method can also remove the inevitable effect of interference to the prevoius method between the second-harmonic waves henerated at the cell windows and the second-harmonic wave to be mesaured. Theoretical expressions have newly been derived to desctibe the mactoscopic nonlinear polatixzations associated with this new configuration. It has been applied to organic molecules, p-NA and MNA, whose hyperploarizabilities were already known and applied to unkown MBA-NP, PNP and DAN. The results of measurement coincide well with the thoretical calcultaions using a P-P-P and a CNDO/S method.2. It has been concluded that the powder method for evaluating a figure of merit of second-order nonlinearity of crystals should not be utilized for the organic crystals, since the coherence lengths of such crystals with well-aligned molecules are too short. Only ceystals with molecules nearly parallel to each other could surpass d33 of LN, which was used for and efficient frequency doubler of a semiconductor laser in the form of a waveguide devices. The new of or improved method instead of the powder method is needed in order to seek easily useful organic materials.3. For flaky crystals, whose hyperpolarizabilities large enough, two procedures have been proposed to estimate htier figure of merit. One, for crystals with an optical grade, is to measure the refractive indices by means of a spectrometer or an ellipsometry, and the other, for crystals with an optically deteriorated grade, is to analyze and to know the orientation of molecules in the crystal by an X-ray method. Both procedures have been found to be comlimentary, from the results of measurement of MBA-NP and DAN.