【作者】 李霞；

【导师】 侯洵； 姚保利；

【作者基本信息】 河南大学 ， 光学， 2004， 硕士

【摘要】 聚苯胺(PAn)类和聚对苯撑乙烯(PPV)类材料都为线性共轭高分子有机聚合物。由于这两类聚合物具有良好的导电和发光性能，近几年的研究主要集中在制备光电器件、发光二极管等方面上，对其光学非线性的研究报道甚少。但它们都具有易离域化的π-共轭电子结构，通常显示出常规高分子所不具有的独特非线性光学性质。例如较大的非线性系数、较快的光学响应速度、良好的化学和热稳定性；并且结构易于剪裁，可以通过分子设计改变主链或侧链的结构来优化材料的性能；其原料价格低，易于大量制取。这些优异的特性使得该聚合物材料在高速光开关、光存储、光限幅器、光计算和光通讯等领域具有潜在的应用价值。 本文研究了PAn类和PPV类两类聚合物的三阶非线性光学特性。以N-甲基吡咯烷酮(NMP)为溶剂，制得PAn／NMP溶液和甲基取代PAn／NMP溶液；以氯仿为溶剂，制得2-甲氧基5-丁氧基取代PPV／氯仿溶液和2-甲氧基5-癸氧基取代PPV／氯仿溶液。 实验方面，测量了所用样品的吸收光谱。采用Z-扫描法对样品进行了闭孔、开孔Z-扫描实验，但未测出开孔Z-扫描曲线，说明样品溶液的非线性吸收非常小，可以忽略不计。根据闭孔Z-扫描曲线估算了样品的非线性折射率。对2-甲氧基5-丁氧基取代PPV／氯仿溶液进行了激光诱导自衍射实验，根据衍射环的个数估算出了样品的非线性常数；同时还对该样品进行了光限幅特性的研究，由实验结果分析得出：由光热效应引起的自衍射是产生光限幅特性的主要机制。 理论方面，以菲涅尔—基尔霍夫衍射理论为基础，建立了非线性介质对高斯光束的衍射模型，对高斯光束通过非线性介质后的传输行为进行了详细的理论推导和数值计算，从一种新的角度解释了Z-扫描现象，是计算非线性折射率和双光子吸收系数的一种新方法。数值模拟计算表明：对于不考虑双光子吸收的闭孔Z-扫描曲线，在小的非线性相移的情况下，其结论与经典的Z-扫描理论完全一致，同时还得到了常规Z-扫描理论无法得到的新的计算结果。对于考虑双光子吸收的河南大学光学专业2001级硕士论文闭孔Z一扫描曲线，其结果与经典的Z一扫描理论的结果也完全一致。而对于已给定的开孔Z一扫描曲线，用该理论计算出的双光子吸收系数是经典开孔Z一扫描理论计算值的1/3，其它结论与传统Z一扫描理论完全吻合。该理论的近似条件只要求薄样品和小非线性吸收，比传统理论具有更好的准确性。该理论推导出了考虑双光子吸收的闭孔和开孔Z一扫描曲线的统一公式，这是传统Z一扫描理论无法给出的。这种理论方法也是研究高斯光束通过非线性介质后传输特性的一种很好的方法。更多还原

【Abstract】 Polyaniline (PAn) and Poly-phenylene vinylene (PPV) are organic polymers with π^-conjugated structure. Due to their good electric conduction and luminescence, people investigate mainly preparation of photoelectric devices and luminescent diodes in these years. Less studies on nonlinear optical properties were reported. However, because of the easily delocalized n electrons , they have more significantly different optical properties than common polymers, such as large third-order nonlinear optical susceptibilities , ultrafast optical response time , good chemical and thermal stabilities. The material properties can be improved through the modification of the backbone and side chain thanks to their easily being cut out. These organic polymers are tended to manufacture because of low price of materials. Therefore they have widely potential application in optical switch, optical storage, optical limiter, optical computation and communication.The third-order nonlinear optical properties of two kinds of π-conjugated polymer, Polyaniline and Poly-phenylene vinylene, were studied. Using N-methyl-pyrrolidone (NMP) as solvent, we prepared PAn/ NMP solution and methyl-replaced PAn/NMP solution. Using chloroform as solvent, we prepared 2-methoxy-5-butoxy-PPV /chloroform solution and 2-methoxy-5-decoxy-PPV /chloroform solution.On experimental, the absorption spectra of the samples were measured. We carried out closed-aperture and open-aperture Z-scan experiments. But we did not obtain the open-aperture Z-scan curve, which indicate that the samples’ nonlinear absorption are extremely small, therefore the nonlinear absorption could be neglected. The nonlinear refraction index n2 were estimated according to the closed-aperture Z-scan curves. We also did the laser-induced self-diffraction experiment on 2-methoxy-5-butoxy-PPV. Nonlinear constant r| could be calculated according to the numbers of thediffraction rings. The sample’s optical limiting properties were discussed. According to the experimental results, we estimated that the main mechanism of the optical limiting was from the thermo-optic effect.On theoretical, a diffraction model of a nonlinear optical medium to a Gaussian beam was built based on Fresnel-Kirchhoff diffraction theory . The propagation behavior of the Gaussian beam passing through the nonlinear optical medium was theoretically deduced and numerically simulated, which could explain the Z-scan phenomenon from a new approach. It provides a new way to calculate the nonlinear refraction index and the two-photon absorption coefficients. Numeric simulation showed that for the closed-aperture Z-scan considering the two-photon absorption, the simulation results were well consistent with the conventional theory. For a given open-aperture Z-scan curve, the two-photon absorption coefficient computed by the new Z-scan theory was 1/3 of the value fitted by the conventional Z-scan theory, whereas other conclusions were identical to the conventional Z-scan theory. This theory has better accuracy than the conventional Z-scan theory because the approximate conditions are only thin sample and small nonlinear absorption. From this theory, a unified equation was derived, which could describe both the closed-aperture Z-scan curve and the open-aperture Z-scan curve with consideration of the two-photon absorption. This can not be given by the conventional Z-scan theory. This theory is also a good method for studying propagation properties of the Gaussian beam passing through the nonlinear media.更多还原