Classical Wave Propagation In Two-dimensional System And The Organic Polymer Polarization Reversal Phenomenon

This thesis includes two parts. In the first part from Ch.1 to Ch.5, Plane Wave Method (PWM) and Multiple Scattering Theory (MST) are used to study the classical wave propagations through two-dimensional periodic and random media. In the second part from Ch.6 to Ch.8, the peculiar phenomena called Photoinduced Polarization Inversion (PIPI) in organic polymer is discussed.Photonic Crystal (PC) is a new concept and material first proposed in the late 80s of last century, which makes it possible for us to control the motion of photon. And its extensive potential applications attract many scientists into this field which, as a result, developed quickly in the last tens of years.By making use of complete bandgaps, people can model the propagation of light and produce some useful devices, such as fiber, micro-cavity by PC. In Section I of Ch.4, the light-guiding properties of partial bandgaps are studied. Our results show the partial bandgaps can also be used to control the light flow effectively. Compared with complete bandgaps, the later does not require fabricating line defect in micro-crystals, which may make the manufacture of devices much easier.Recently, the focusing image by PC slab has been a hot topic. Although increasing numbers of related literatures concerning this topic, no convincing mechanism is proposed so far. On the topic, there are two kinds of mainstream opinions:(1) the focusing image comes from the negative effective refraction index of PCs;(2) the focusing image is a result of negative-definite photonic effective mass rather than the negative effective refraction index. Due to the similarity of waves, the concept of PCs can be extended to other classical wave systems. Considering the system consisted of steel cylinders located squarely in air, we exhibit the focusing image might be caused by self-collimating effect. Therefore, in our opinion, the reported claims on focusing image are not conclusive; further confirmations are needed to interpret this interesting phenomenon. The results was published onAppl Phys. Lett, Vol. 85, No. 6, 2004, and one of the figures was cited as Cover Image of this issue (refer to page 119 in the thesis). For more details, please refer to Section II in Ch.4.In 1999, Torres et al. reported the first observation of Bloch waves and localized states in surface water wave system. The late theoretic results agreed well with the experiments. Unfortunately, no complete bandgaps were observed in the experiments. Motivated by their results, we explore the band structure of surface water wave over bottoms embedded with squarely arranged steps. The results show that only when the steps are very close to the water surface, do the complete bandgaps appear. By introducing the Phase Diagram Technique developed by Ye et al., we further study the localization phenomena in water wave system, and find that when localization occurs, not only is the energy localized, but the phase of wave appears to be collectively consistent. Those observations fully comply with the previous prediction that the localization is a collective coherent state.In the second part, organic polymer is studied. Traditionally, organic polymer was the field of chemists. However, in recent years, its novel physical and chemical properties attracted the attention of scientists from other fields, and a new interdisciplinary frontier — Organic Functional Materials and Devices, was developed.In conventional inorganic materials, the carriers are electrons or holes with both charge and spin. Yet in organic materials, the carriers can be soliton with separated charge and spin, or polaron with both charge and spin, or bipolaron with two units of charge but no spin. All those carriers are the collective elementary excitations caused by electron-lattice interaction. Thereby, we can expect some peculiar phenomena in organic materials absent in inorganic materials, such as the carrier fission, Schrodinger cat state. In Ch.6 and Ch.7, some related concepts and theories are introduced.In 2000, Sun et al. pointed out that, through photoexcitation, the Exciton in a single molecule with positive polarizability can be excited into Biexciton with negative polarizability, and an ultrafast molecule switch can be realized by making...