【作者】 刘晓东；

【导师】 侯蓝田； 王慧田；

【作者基本信息】 燕山大学 ， 电路与系统， 2002， 博士

【摘要】 本论文针对中红外材料的特点，建立了三类无序介质的中红外光子局域化理论；针对测量材料三阶光学非线性系数的Z-扫描技术的应用实际，研究了具有大的非线性吸收材料的Z-扫描透过率曲线特征；系统地研究了光阑孔径对Z-扫描透过率曲线轮廓的定量影响。本论文在科学与专门技术方面都取得了一些有创造性的成果，现摘要如下： 首先，选取了几种高折射率的中红外材料和中红外透明基质材料，并建议使用它们和其它一些从未使用过的材料来进行光子局域化研究，突破了“锗(Ge)是进行光子局域化实验的最佳材料”的传统观念：对中红外无序光学介质进行了探索性地科学分类，并避开了高浓度散射体情况下使用的众多复杂且不成熟的理论模型，基于精确的米氏(Mie)散射理论和低浓度散射体近似，探讨了更有实际意义的低浓度散射体的无序光学介质的光子局域化问题。 其次，在建立第一类无序介质(散射体为无损耗的高折射率电介质球)的中红外光子局域化理论中，发现在散射体与基质的折射率比大于3.1时，单粒子各向异性散射因子在米氏散射共振峰附近出现有利于光子局域化的负值区，突破了米氏共振散射均为前向散射的传统物理观念。计算发现，当散射体浓度为10％，相对折射率大于3.8时开始出现理想的光子局域化。继而，又提出了散射体平均等效散射截面饱和的假设，研究了此假设导致的实现理想光子局域化的困难性。 第三，在建立第二类无序光学介质(散射体为反常色散电介质球)的中红外光子局域化理论中，通过数值法研究发现，在某些反常色散电介质球做散射体的无序介质中可以实现一定意义下(有一定的吸收)的光子局域化，且频率位于各自的剩余射线带内。研究还发现，基质的折射率效应在第二类无序介质中和在第一类无序介质中的作用完全不同。 第四，在建立第三类无序介质(散射体为良导体—金属球)的中红外光子局域化理论中，作者发现，各种金属在中红外区的各个频率点上的散射行为均极为相近，是一种在中红外区反照率高但散射效率较低的散射体；在浓度为10％时，该类介质的局域化参量最小只能达到6.6，几乎不可能实现真正的中红外光子局域化。数值法与解析法研究还揭示了这种金属散射体系统与低吸收、高折射率散射体系统(第一类无序光学介质)间的内在联系，而且基质的折射率效应与第一、第二类无序介质均不同，即体系局域化参量与体系的常用基质材料无关。 第五，在研究大的非线性吸收材料的Z-扫描实验曲线特征时，作者发现，常见的峰-谷或谷-峰结构特征取决于材料的三阶非线性极化率的虚部与实部的比值ρ，并且提出了“决定峰-谷或谷-峰结构存在与否的临界值ρ_c”的概念。作者求得了高斯光束情况下的精确临界值，以及曲线的某些特征参量与上述比值的关系和理论的适用范围，所做的CS。的乙扫描实验与理论符合得很好。同时，本文还对“逐点相除法”求非线性折射相移的合理性进行了论证。 第六，在研究光阑的大小S对Z．扫描实验曲线轮廓的定量影响时，提出了对于给定材料“决定峰－谷或谷－峰结构存在与否的临界孔径值y”的概念，并且用数值方法给出了高斯光束下S与尸以及pC与S的定量关系。作者用CS。所做的不同孔径时的乙扫描实验很好地验证了这些定量关系。 另外，在用红外光谱仪进行以a－SIC为散射体、以KBr为基质的无序介质的光子局域化实验时，意外地发现了一个与Christiansen效应有关的新物理现象。本文用LorentZ色散模型对此现象给出了精确的解释，并对该现象在制造新型的带通滤波器和测定某些材料的折射率等方面的应用做了很深入的探讨，这是在研究过程中发现并开辟了的一个新的研究方向。更多还原

【Abstract】 The dissertation, for the first time to our knowledge, establishes a systematic theory of mid-infrared photon localization for three kinds of random media in view of the properties of the mid-infrared materials, explains an interesting phenomenon newly found by the author, studies comprehensively the characteristics of Z-scan transmittance curves for the materials with a large nonlinear absorption in connection with the practical applications of Z-scan technique, researches numerically into the quantitative influence of the aperture size and nonlinear absorption on the profile of the Z-scan transmittance curves. Several creative achievements in respect of science and technique are contained in this dissertation, and summarized as follows:First, the author points out, for the first time to our knowledge, that several mid-infrared materials with large refractive index and low absorption and some transparent matrices in the mid-infrared can be used for the investigations on the mid-infrared photon localization, and breaks the idea that only Germanium (Ge) is the best material for experiments searching the photon localization.Second, in the theory of mid-infrared photon localization in the random media with high-refractive-index and lossless scatterers, which is called the first kind of random media, the author finds out that a negative-value region of the asymmetric scattering factor appears in the vicinity of Mie-resonant scattering peaks when the relative refractive index of the scatterer to the matrix is larger than 3.1, and breaks the conventional physical concept that Mie scattering is predominant in the forward direction. The study indicates that ideal photon localization establishes when the relative refractive index of the scatterer is larger than 3.8 and the concentration of the scatterers is as low as 10% using the Mie scattering theory and the low concentration approximation. In the meanwhile, a new concept called effective scattering cross section saturation is put forward, and the difficulty of perfect localization of mid-infrared radiation is discussed if effective scattering cross section may become saturate.Third, in the theory of mid-infrared photon localization hi the random media with anomalous dispersive dielectric scatterers, which is called the second kind of random media by our group, the author finds numerically out that mid-infrared photon localization hi a sense may establish in this kind of random medium, and the localization frequencies are in the reststrahlen band of the anomalous dispersive scatterer. For the first time, it is found that the influence of the refractive index of the background matrix on the photon localization in the first kind of random medium is very different from the one in the second kind of random medium.Forth, in the theory of mid-infrared photon localization in the random media using metal particles as random scatterers, which is called the third kind of random media, the author finds out that the scattering behavior of every metal in mid-infrared region is similar to each other, and all types of metal particles are low-efficiency scatterers but with high extinction albedo. When the concentration of the metal particles is 10%, 6.6 is the smallest value of the localization parameter, therefore photon localization can not be attained in this kind of random medium although the scattering is also strong and low-absorptive. It is revealed that this system has an intrinsic relationship with the one with high-refractive-index and low-absorptive scatterers, and influence of the refractive index of the matrix on the photon localization in this kind is very different from the other two, that is, the localization parameter be independent of the refractive index of the lossless matrix used commonly.Fifth, when studying closed-aperture Z-scan experimental transmittance curve of the materials with relatively large third-order nonlinear absorption, the author finds out that the well-known peak-valley or valley-peak structure is dependent on the relative value p更多还原