The Quantum-Optical Phenomena

On the contrary, the semiclassical approach in the problem of the optical absorption is restricted to a great extent and the adequate description of the phonon-assisted optical bands with a complicated structure caused by the dynamic JTE cannot be done in the framework of this approach [13]. An expressive example is represented by the two-humped absorption band of A —> E <8> e transition. The dip of absorption curve for A —> E <8> e transition to zero has no physical meaning because of the invalidity of the semiclassical approximation for this spectral range due to essentially quantum nature of the density of the vibronic states in the conical intersection of the adiabatic surface. This result is peculiar for the resonance (optical) phenomena in JT systems full discussion of the condition of the applicability of the adiabatic approximation is given in Ref. [13]. 

Until now, our discussions have been based on the classical Galileo-Newton representations. Moving on to quantum-optical phenomena and others, these ideas appear to be insufTicient and it is necessary to consider some more general notions, in particular, Einstein s special theory of the relativity (STR, 1905). 

Many phenomena in solid-state physics can be understood by resort to energy band calculations. Conductivity trends, photoemission spectra, and optical properties can all be understood by examining the quantum states or energy bands of solids. In addition, electronic structure methods can be used to extract a wide variety of properties such as structural energies, mechanical properties and thennodynamic properties. 

Although we admit that these effects must surely appear in small particles, we cannot countenance the uncritical invocation of vague and esoteric quantum size effects, as is sometimes done, to dispose of optical phenomena in small particles that are not understood. Often the correct interpretation may be much simpler particle shape, for example, which we shall discuss in Sections 12.3 and 12.4. Our best advice, based on calculations (Martin, 1973 Chen et... 

In summary, we have experimentally demonstrated laser control of a branching photochemical reactions using quantum interference phenomena. In addition we have overcome two major experimental obstacles to the general implementation of optical control of reactions (a) we have achieved control using incoherently related light sources, and (b) we have affected control in a bulk, thermally equilibrated, system. 

Since many of these developments reach into the molecular domain, the understanding of nano-structured functional materials equally necessitates fundamental aspects of molecular physics, chemistry, and biology. The elementary energy and charge transfer processes bear much similarity to the molecular phenomena that have been revealed in unprecedented detail by ultrafast optical spectroscopies. Indeed, these spectroscopies, which were initially developed and applied for the study of small molecular species, have already evolved into an invaluable tool to monitor ultrafast dynamics in complex biological and materials systems. The molecular-level phenomena in question are often of intrinsically quantum mechanical character, and involve tunneling, non-Born-Oppenheimer effects, and quantum-mechanical phase coherence. Many of the advances that were made over recent years in the understanding of complex molecular systems can therefore be transposed and extended to the study of... 

The Raman spectra are quicker and easier to determine than the infrared absorption spectra because ordinary optical equipment can be used, but frequently they are more difficult to interpret. The quantum restrictions in the two phenomena, particularly for symmetrical molecules, are not always the same, because the Raman spectrum involves an intermediate excited state of the molecule. For this reason, it is desirable to have the data of both Raman and infrared absorption spectra in order to determine completely the rotational and rotational-vibrational energy levels in the molecule. The Raman spectrum can be obtained in some solutions where direct absorption measurements are impossible because the solvent is opaque in the infrared. Aqueous solutions offer a good example of such a case. 

More General Treatments of Electron Correlation in Polymers.—The introduction of excitonic states was just a simple example to show how one can go beyond the HF approximation to obtain correlated electron-hole pairs, whose energy level(s) may fall into the forbidden gaps in HF theory, and form the basis for interpretation of optical phenomena in semiconducting polymers. The schemes described until now for investigation of certain types of correlation effects (the DODS method for ground-state properties and the exciton-picture for excited states) are relatively simple from both the conceptual and computational points of view and they have been actually used at the ab initio level. It is evident, on the other hand, that further efforts are needed in polymer electronic structure calculations if we want to reach the level of sophistication in correlation studies on polymers which is quite general nowadays in molecular quantum mechanics. 

Solid state photonic devices are a class of devices in which the quantum of light, the photon, plays a role. They function by utilizing the electro-optical and/or opto-electronic effects in solid state materials. Because the interband optical transition (absorption and/or emission) is involved in photonic phenomena and... 

The complete description of luminescence as a complex electronic-optical phenomenon is possible only within the framework of quantum electrodynamics. These xoblems are considered in well-known monographs by Vavilov Levshin Feofilov, Stepanov Prinsgheim and original pap s by Levshin Perrin and Webra But as other optical phenomena occurring on the atomic or molecular... 

The virtually unlimited possibilities offered by organic chemistry in tailoring specific properties of PFs will give access to new polymeric systems which show remarkable and unexpected properties. As demonstrated in this chapter, SMS will be a valuable tool in answering scientific questions and will no doubt provide the experimental demonstration of many new phenomena. Ultimately, conjugated polymers may even prove versatile systems for sophisticated quantum optical experiments, due to the strong control over polarisation enabled by their anisotropic structure. 

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