【作者】 李芳；

【导师】 郑启光； 陆培祥；

【作者基本信息】 华中科技大学 ， 物理电子学， 2008， 博士

【摘要】 近年来,传统意义上的染料,因为它们特殊的光、电、磁等性质在高新技术领域得到广泛的应用,成为“功能性染料”而获得迅速发展。在已知的“功能性染料”中,酞菁以其独特的物理、化学性能而备受瞩目。其中,金属酞菁作为一种很有发展前途的有机非线性光学材料,特别引起了人们浓厚的研究兴趣。本文主要利用单光束纵向Z扫描技术,对几种金属酞菁化合物进行了非线性光学吸收特性和光限幅特性的实验和理论研究。全文的主要研究内容、结论与创新性如下:（1）介绍了非线性光学性质测量的Z扫描技术。详细分析了Z扫描技术的原理和Z扫描技术的理论计算过程,讨论了Z扫描测量的影响因素,为全文的实验研究提供了理论依据。（2）对两种金属酞菁的电子结构和电子光谱用量子化学的方法进行了研究。以量子化学计算软件Hyperchem为工具,用PM3半经验方法和ZINDO/S方法计算研究了铜酞菁和钴酞菁的电子结构和电子光谱,并定性的归纳总结了总电子数为奇数的这类金属酞菁的可见最大吸收峰(λ_max)与分子结构的关系。研究结果表明:在优化的分子几何构型基础上计算得到的电子光谱与实验值很吻合;并且λ_max与OWF_π-π（π-π）重叠加权因子,表征分子共轭程度大小)之间存在很好的线性关系。这为寻找分子结构对材料光学性能的影响规律,合成新型非线性光学材料提供了理论依据。（3）对金属酞菁溶液进行了非线性光学吸收特性和光限幅特性的实验和理论研究。首先采用单光束纵向Z扫描技术用飞秒振荡级激光研究了铜酞菁溶液的非线性光学吸收特性,详细讨论了入射激光功率对非线性吸收的影响和溶液浓度对非线性吸收的影响。研究结果表明,铜酞菁溶液总体表现出反饱和吸收（RSA）效应,这主要是由材料的三光子吸收（3PA）引起;并且在铜酞菁溶液浓度较低时,随着入射激光功率增大,样品溶液的RSA效应越强,而对于浓度比较大的铜酞菁溶液,随着入射激光功率增大,样品溶液的RSA效应越强,但入射激光功率增大到一定程度,样品溶液出现“光褪色”现象,RSA效应趋于饱和,并开始减弱。然后用1064 nm Nd:YAG连续激光研究了铜酞菁溶液和多氯代铜酞菁溶液的光限幅特性,根据稳态的速率方程理论分析表明,铜酞菁溶液和多氯代铜酞菁溶液的光限幅效应主要是由材料的三重激发态吸收引起的RSA造成的。（4）对金属酞菁薄膜进行了非线性光学吸收特性和光限幅特性的实验和理论研究。采用单光束纵向Z扫描技术用800nm飞秒放大级激光研究了铜酞菁薄膜的非线性光学吸收特性以及光限幅特性。在开孔的Z扫描实验中,观察到了SA向RSA转变的现象。理论上提出了飞秒超短超快脉冲作用有机分子的有效四能级模型,并从动态速率方程理论出发,分析讨论了此种条件下产生非线性光学吸收特性的物理机制,而且提出了SA与RSA相互转化的阈值光强理论。研究结果表明,当入射光强达到转变的阈值光强时,由于CuPc分子的高阶激发态发挥作用,使样品中的五阶非线性效应增强,导致了SA向RSA的转变。同时该研究也表明,铜酞菁薄膜有较大的五阶非线性吸收系数β^（5）(0.24×10^-21 cm³/W²),对800 nm飞秒激光具有很好的光限幅效应,是一种非常有潜力的光限幅材料。更多还原

【Abstract】 The traditional dyes have been growing rapidly as "functional dyes" because of their special properties of optics,electronics and magnetism in the field of high-tech.In the known "functional dyes",phthalocyanines have attracted a great deal of attentions due to their unique physical and chemical properties.Among them,the metal-phthalocyanine,as a very promising organic nonlinear optical material,has particularly aroused strong research interest.In this dissertation,experimental and theoretical studies on the nonlinear absorption properties and optical limiting properties of metal-phthalocyanine are performed mainly by the sensitive single-beam z-scan technique using the femtosecond laser.The main contents,research conclusions and innovations are summarized as following:（1） The z-scan technique used for the measurement of nonlinear optical properties is presented.The principle and theoretical calculation process of z-scan technique are analyzed in detail,and the influence factors in the z-scan measurement are disscused, which provide a theoretical basis and instruction for the experimental researches in the dissertation.（2） The electronic structures and electronic spectra of two metal-phthalocyanines are studied by quantum chemical caculation.Using the Hyperchem software,the geometrical molecular structures of cobalt phthalocyanine and copper phthalocyanine are firstly optimized by the semi-empirical PM3 method and the electronic spectra are then calculated by the ZINDO/S method,and the relationship between the visible absorption maximum(λ_max) and the molecular structure of phthalocyanines with odd total electron numbers is concluded qualitatively.The results show that the calculated electronic spectra based on the optimized geometrical molecular structures are well consistent with the experimental values.OWF_π-π（π-πoverlap weighting factor,which is considered as a measurement of the extent ofπ-electron delocalization） andλ_max is in well linear relationship.The study of seeking the relationship between the molecular structures and their optical properties provides a theoretical instruction for synthesizing new nonlinear optical materials.（3） The experimental and theoretical studies on the nonlinear absorption（NLA） properties and optical limiting properties of metal-phthalocyanine solutions are performed. Using the femtosecond seed laser,the NLA properties of copper phthalocyanine solutions are studied by the sensitive single-beam z-scan technique.The relationship between the input laser power and NLA properties,and the relationship between the solution concentration and NLA properties are discussed in detail.The results show that the copper phthalocyanine solutions exhibit reverse saturable absorption（RSA） effect,which mainly originates from three-photon absorption（3PA）;and the RSA effect becomes stronger with the input laser power increasing when the sample solution concentration is low,while for the high concentration sample solution,with the input laser power increasing,the RSA effect first becomes stronger,then becomes saturable,and finally becomes weaker due to the "optical fading" phenomenon.In addition,the optical limiting performances for 1064 nm continual-wave laser of copper phthalocyanine and polychloro copper phthalocyanine solutions have been investigated.The results of the steady-state rate equation analysis show that the good optical limiting performances are mainly attributed to RSA induced by the absorption of triplet excited state.（4） The experimental and theoretical studies on the NLA properties and optical limiting properties of metal-phthalocyanine thin film are performed.Using femtosecond regenerative amplifier laser,the NLA properties and optical limiting properties of copper phthalocyanine thin film are investigated by the sensitive single-beam z-scan technique.In the open-aperture（OA） z-scan measurements of the film,a transition from saturable absorption（SA） to RSA is observed as the excitation intensity is increased.An efficient four-energy-level model for the organic materials excited by femtosecond pulse laser is developed,and based on which the dynamic rate equation analysis is performed and the intensity dependence of level populations is obtained,which reveals the source of NLA. The results show that the transition from SA to RSA is ascribed to the fifth-order effect of excited-state absorption（ESA） induced by two-photon absorption（TPA） process when the input laser intensity reaches a critical value.Furthermore,it is found that the copper phthalocyanine thin film possesses a large fifth-order absorption coefficientβ⁵ (0.24×10^-21cm³/W²).It indicates that the copper phthalocyanine thin film could be a very promising candidate for optical limiting material.更多还原