Raman spectroscopy linear

Laubereau A 1982 Stimulated Raman scattering Non-Linear Raman Spectroscopy and its Chemical Applications ed W Kiefer and D A Long (Dordrecht Reidel)... 

A. B. Harvey, ed., Chemical Applications of Non-linear Raman Spectroscopy, Academic Press, New York, 1981. 

Thus far, we have reviewed basic theories and experimental techniques of Raman spectroscopy. In this chapter we shall discuss the principles, experimental design and typical applications of Raman spectroscopy that require special treatments. These include high pressure Raman spectroscopy, Raman microscopy, surface-enhanced Raman spectroscopy, Raman spectroelectro-chemistry, time-resolved Raman spectroscopy, matrix-isolation Raman spectroscopy, two-dimensional correlation Raman spectroscopy, Raman imaging spectrometry and non-linear Raman spectroscopy. The applications of Raman spectroscopy discussed in this chapter are brief in nature and are shown to illustrate the various techniques. Later chapters are devoted to a more extensive discussion of Raman applications to indicate the breadth and usefulness of the Raman technique. 

If coherent radiation with a very high intensity is applied continuously or as pulse, non-linear effects can be observed which produce coherent Raman radiation. This is due to the quadratic and cubic terms of Eq. 2.4-14, which describe the dipole moment of a molecule induced by an electric field. Non-linear Raman spectroscopy and its application are described in separate chapters (Secs. 3.6 and 6.1), since this technique is quite different from that of the classical Raman effect and it differs considerably in its scope. 

The importance of the hyper Raman effect as a spectroscopic tool results from its symmetry selection rules. These are determined by products of three dipole moment matrix elements relating the four levels indicated in Fig. 3.6-1. It turns out that all infrared active modes of the scattering system are also hyper-Raman active. In addition, the hyper Raman effect allows the observation of silent modes, which are accessible neither by infrared nor by linear Raman spectroscopy. Hyper Raman spectra have been observed for the gaseous, liquid and solid state. A full description of theory and practice of hyper-Raman spectroscopy is given by Long (1977, 1982). 

One of the main advantages of CARS and also of other nonlinear Raman spectroscopies is the high resolution that can be achieved in spectra of gases at low pressures. The reason for this is that the instrumental resolving power in these techniques depends only on the convoluted linewidths of the lasers used for excitation, whereas in linear Raman spectroscopy the resolution is determined by the monochromators used to disperse the observed scattered Raman light. 

In this section mainly results of linear Raman spectroscopy of gases and vapours have been considered and selected examples of the results of nonlinear techniques were included, e.g. CARS or stimulated and inverse Raman spectroscopy, by which much higher resolution can be achieved. Further such investigations have been reviewed elsewhere (Esherick and Owyoung, 1982 Schrotter et al., 1988a, 1988b, 1990 Lavorel et al., 1992). 

Schrotter HW (1982) In Kiefer W, Long DA (eds) Non-linear Raman Spectroscopy and its Chemical Applications. D Reidel, Dordrecht, p 143... 

W. Kiefer, Non-linear-Raman Spectroscopy, Applications, in Encyclopedia of Spectroscopy and Spectrometry, Vd. 2, Academic Press, San Diego 2000,... 

Conventional linear Raman spectroscopy is still widely used to obtain pure rotation, and rotation-vibration, gas phase spectra. There are many references describing such applications in detail [ e.g. 1,2], so nothing more will be said here. Instead we shall consider briefly some new aspects. 

Kiefer, W., and Long, D.A., eds., Non-Linear Raman Spectroscopy and its Chemical Applications, Reidel, Dordrecht, 1982. 

The information obtained from linear Raman spectroscopy is derived from the following experimental data ... 

For sufficiently small electric field amplitudes E the nonlinear terms in (3.18a) can be neglected, and we then obtain (3.2) for the linear Raman spectroscopy. 

The main merit of the stimulated Raman effect for molecular spectroscopy may be seen in the much higher intensities of stimulated Raman lines. During the same measuring time one therefore achieves a much better signal-to-noise ratio than in linear Raman spectroscopy. The experimental realization of stimulated Raman spectroscopy is based on two different techniques ... 

A larger increase of sensitivity in linear Raman spectroscopy of liquids has been achieved with optical-fiber Raman spectroscopy. This technique uses a capillary optical fiber with the refractive index nu filled with a liquid with refractive index He > m. If the incident laser beam is focused into the fiber, the laser light as well as the Raman light is trapped in the core due to internal reflection and therefore travels inside the capillary. With sufficiently long capillaries (1—30 m) and low losses, very high spontaneous Raman intensities can be achieved, which may exceed those of conventional techniques by factors of 10 [8.31]. Figure 8.7 shows schematically the experimental ar-... 

A.C. Eckbreth, P.W. Schreiber Coherent anti-Stokes Raman spectroscopy (CARS) Applications to combustion and gas-phase diagnostics, in Chemical Applications of Non-Linear Raman Spectroscopy, ed. by A.B. Harvey (Academic, New York 1981)... 

Whereas the resolution in linear Raman spectroscopy is limited in principle by the slit width of the spectrometer, a considerable improvement in the instrumental resolution was attained through the development of the techniques of nonlinear or coherent Raman spectroscopy, where the interaction of two laser beams with the third-order susceptibility of the sample creates the spectrum. In this case, the resolution is determined by the convoluted linewidth of the two lasers, the Doppler effect, and pressure broadening of the spectral lines. 

G Tejeda, B Mate, JM Fernandez-Sanchez, S. Montero. Temperature and density mapping of supersonic jet expansions using linear Raman spectroscopy. Phys Rev Lett 76 34-37, 1996. 

HW Schrotter, H Berger, JP Boquillon, B Lavorel, G Millot. High-resolution non-linear Raman spectroscopy of rovibrational bands in gases. J Raman Spectrosc 21 781-789, 1990. 

W Kiefer, DA Long, eds. Non-Linear Raman Spectroscopy and Its Chemical Applications. Dordrecht Reidel, 1982. 

B Lavorel, G Millot, M Rotger, G Rouill6, H Berger, HW Schrotter. Non-linear Raman spectroscopy in gases. J Mol Struct 273 49-59, 1992. 

The importance of the hyper-Raman effect as a spectroscopic tool results from its symmetry selection rules. It turns out that all infrared active modes of the scattering system are also hyper-Raman active. In addition, the hyper-Raman effect allows the observation of silent modes, which are accessible neither by infrared nor by linear Raman spectroscopy. 

A great increase of sensitivity in linear Raman spectroscopy of liquids has been achieved with the optical fiber Raman spectroscopy. This technique... 

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