Raman scattering, spontaneous

The only modification of equation (Al.6.90) for spontaneous Raman scattering is the multiplication by the density of states of the cavity, equation (Al.6.24). leading to a prefactor of the fonn cojCOg. ... 

Conventional spontaneous Raman scattering is the oldest and most widely used of the Raman based spectroscopic methods. It has served as a standard teclmique for the study of molecular vibrational and rotational levels in gases, and for both intra- and inter-molecular excitations in liquids and solids. (For example, a high resolution study of the vibrons and phonons at low temperatures in crystalline benzene has just appeared [38].)... 

The scattered radiation V3 is to high wavenumber of Vj (i.e. on the anti-Stokes side) and is coherent, unlike spontaneous Raman scattering hence the name CARS. As a consequence of the coherence of the scattering and the very high conversion efficiency to V3, the CARS radiation forms a collimated, laser-like beam. 

The selection mles for CARS are precisely the same as for spontaneous Raman scattering but CARS has the advantage of vastly increased intensity. 

Laser-based methods of identification are extremely powerful they are able to provide species and structural information, as well as accurate system temperature values. Spontaneous Raman scattering experiments are useful for detection of the major species present in the system. Raman scattering is the result of an inelastic collision process between the photons and the molecule, allowing light to excite the molecule into a virtual state. The scattered light is either weaker (Stokes shifted) or... 

Relation Between Coherent and Spontaneous Raman Scattering... 

X lT + E r Xij ki, which refer in their order of appearance to the Cartesian polarization components of the CRS, pump, probe, and Stokes fields in the four-wave mixing process [31]. In transparent and optically inactive media, where the input frequencies are away from any electronic transition frequencies, and only the molecular ground state is populated, the selection rules of both resonant coherent and spontaneous Raman scattering are identical... 

Accordingly, for a given Raman-active resonance r, the amplitudes of XijM can be expressed in terms of the isotropy and symmetric anisotropy invariants of the corresponding spontaneous Raman scattering tensor, a2 and 7S2, respectively. In the case of frequency-degenerate CRS considered here, the two relevant independent tensor components assume the following form [33, 34] ... 

In this chapter, we focus on nonresonant spontaneous Raman scattering. A special case of Raman scattering, surface-enhanced Raman spectroscopy (SERS), is discussed in Chapter 15. 

The inelastic processes - spontaneous Raman scattering (usually simply called Raman scattering), nonlinear Raman processes, and fluorescence - permit determination of species densities as well as temperature, and also allow one, in principle, to determine the temperature for particular species whether or not in thermal equilibrium. In Table II, we categorize these inelastic processes by the type of the information that they yield, and indicate the types of combustion sources that can be probed as well as an estimate of the status of the method. The work that we concentrate upon here is that indicated in these first two categories, viz., temperature and major species densities determined from vibrational Raman scattering data. The other methods - fluorescence and nonlinear processes such as coherent anti-Stokes Raman spectroscopy - are discussed in detail elsewhere (5). 

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