Raman scattering, description

Additionally, the description of LC involves an analysis of order. In particular, a sharp drop of the order parameter to B is observed when a transition takes place from the LC phase into the isotropic phase. The order parameter can be measured experimentally in a number of ways, such as diamagnetism, birefringence, Raman scattering, NMR, and EPR. 

The discussion of intensities necessitates the quantum chemical description of infrared absorption and Raman scattering.23 Such a description helps in understanding the electromagnetic processes that occur in molecules, but... 

To aid the general reader, short descriptions of the fundamentals of modern Raman scattering and attenuated total reflection (ATR) infrared spectroscopy are provided. This is followed for each spectroscopy by brief introductions to the enhancement mechanism involved. 

Up to now/ the dimer laser system has been described alone in terms of population inversion between suitable energy levels/ and for this description the condition S2 > A 2 is indeed the only necessary condition for cw laser oscillation/ as long as the thermal population density in the lower laser level remains negligibly low. However/ as this optically pumped laser system is a coherently excited three level system/ the coherent emission can also be described as stimulated Raman scattering/ which is resonantly enhanced by the common level 3 of the pump and laser transitions. This coupled two photon or Raman process does not require a population inversion between levels 3 and 2 and introduces qualitatively new aspects which appreciably influence and change the normal laser behaviour. For a detailed and deeper description of the coherently excited three level dimer... 

In a Raman scattering experiment, the frequency, wave vector, and polarization of incident light (usually from a laser source) are known. Analysis of scattered light frequency, polarization, and relative intensity provides information on properties of elementary excitations in the material under study. General description of the Raman process as well as details of Raman instmmentation can be found elsewhere [108-110, 118]. 

In this paper, we report on simultaneous consideration of incident field enhancement and local density of photon states enhancement near a metal particle with spherical shape as a reasonable primary model for single molecule Raman spectroscopy. Joint action of these two factors at the same point of space is found to offer up to lO -fold enhancement of Raman scattering rate. To the best of our knowledge this is the first evidence that consistent theory of single molecule Raman spectroscopy and comprehensive description of so-called hot points in surface enhanced spectroscopies can be constructed without necessarily involvement of chemical mechanisms. 

The Purcell s original idea [10] on modification of photon spontaneous emission rate is extended to modification of photon spontaneous scattering rate. Simultaneous account for local incident field and local density of photon states enhancements in close proximity to a silver nanoparticle is found to provide up to lO -fold Raman scattering cross-section rise up. Thus, single molecule Raman detection is found to be explained by consistent quantum electrodynamic description without chemical mechanisms involved. 

Up to now all experimental facts of reduction and oxidation are consistent with this model and some conclusions can be drawn. However, a quantitative description by an extended polyelectrolyte theory is necessary, in combination with results of surface spectroscopy.From a recent study of surface-enhanced Raman scattering of native CT-DNA (ds) and denatured DNA (ss) at a Ag-electrode the following conclusions may be drawn ... 

So far, the theory has concentrated on the molecular scattering aspect of coherent Raman scattering. There is still a lot more physics to consider in order to complete the description of the phenomenon in bulk samples but we shall make do with a brief sketch. From Maxwell s equations, the following complex expression can be obtained describing the propagation of plane light waves in the medium [6] ... 

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