Raman scattering instrumentation

Long, M.B., Multi-Dimensional Imaging in Combusting Flows by Lorenz-Mie, Rayleigh and Raman Scattering, Instrumentation for Flows with Combustion (Taylor, A.M.P.K., ed.), Academic Press, 468-508 (1993). 

It is not in the scope of the present chapter to review all possible experimental setups for the various types of Raman scattering classical, microprobe, Fourier transform (FT), coherent anti-Stokes (CARS), surface enhanced (SERS), hyper (HRS), photo-acoustic (PARS), and so forth (see, e.g.. Refs. 29-31). A basic Raman-scattering instrument requires a laser-light source, an appropriate sample holder, a sample illumination optical unit, a scattered-light collection optical unit (these two may be combined in one system), a disperser (spectrometer) or an interferometer, a light detection unit, a recorder, and an appropriate microcomputer able to drive, control, and record all of the experimental parameters as well as the results and their processing. 

Figure 24 illustrates the schematic representation of a confocal-scanning spectral-imaging Raman-scattering instrument, allowing one to draw a mapping of the sample under study. 

In several cases, the samples are not available for study in a laboratory Raman-scattering facility (e.g., stained glasses in churches) one must then proceed to in situ studies. Remote Raman-scattering instruments have been developed for this purpose they use optical fibers technologies as illustrated in Fig. 25. 

With the microfocus instrument it is possible to combine the weak Raman scattering of liquid water with a water-immersion lens on the microscope and to determine spectra on precipitates in equilibrium with the mother liquor. Unique among characterization tools, Raman spectroscopy will give structural information on solids that are otherwise unstable when removed from their solutions. 

Fig. 10. Scattered light including ghosts appearing in a single, double, and triple monochromator. Although scattered light plunges to the square root in a double monochromator, interference with Raman spectra still occurs occasionally. In a triple monochromator, instrumental scatter has never been known to interfere with Raman scatter...

Raman scattering is essentially undelayed with respect to the arrival of the incident light, in this technique the detector is activated only during each laser pulse and deactivated at all other times. This allows only Raman signals to be recorded but fluorescence signals and detector noise are gated out (Fig. 19). Improvement in Raman signal to fluorescence ratio has been achieved as illustrated in Fig. 20. The technique, however, at present seems to be restricted by several instrumental limitations [37). 

If the resolving capacity of the instruments is ideal then vibrational-rotational absorption and Raman spectra make it possible in principle to divide and study separately vibrational and orientational relaxation of molecules in gases and liquids. First one transforms the observed spectrum of infrared absorption FIR and that of Raman scattering FR into spectral functions... 

Vo-Dinh T., Stokes D.L., Griffin G.D., Volkan M., Kim U.J., Simon M.I., Surface-enhanced Raman scattering (SERS) method and instrumentation for genomics and biomedical analysis, J. Raman Spectrosc. 1999 30 785-793. 

Fluorescence, 3 256 22 716. See also EDXRF instruments Micro X-ray fluorescence (MXRF) analysis Total reflection X-ray fluorescence spectrometry micro X-ray, 26 437-439 Raman scattering and, 21 324, 325 sensors using, 22 271... 

The most often used detection method for the optical sensors are based on absorption, luminescence, reflectance, and Raman scattering measurements. The basic theory and instrumentation of most of these... 

M.J. Pelletier, New developments in analytical instruments Raman scattering emission spectrophotometers, in Process/Industrial Instruments and Controls Handbook, G.K. McMillan and D.M. Considine (Eds), McGraw-Hill, New York, 1999. 

The measurement of vibrational optical activity requires the optimization of signal quality, since the experimental intensities are between three and six orders of magnitude smaller than the parent IR absorption or Raman scattering intensities. To date all successful measurements have employed the principles of modulation spectroscopy so as to overcome short-term instabilities and noise and thereby to measure VOA intensities accurately. In this approach, the polarization of the incident radiation is modulated between left and tight circular states and the difference intensity, averaged over many modulation cycles, is retained. In spite of this common basis, there are major differences in measurement technique and instrumentation between VCD and ROA consequently, the basic experimental methodology of these two techniques will be described separately. 

Djaker, N., Lenne, P. F., Marguefi D., Colonna, A., Hadjur, C., and Rigneault, H. 2007. Coherent anti-Stokes Raman scattering microscopy Instrumentation and applications. Nucl. Inst. Meth. Phys. Res. A 571 177-81. 

Cheng, J. X., and Xie, X. S. 2004. Coherent anti-Stokes Raman scattering microscopy Instrumentation, theory, and applications. J. Phys. Chem. B 108 827 0. 

Raman spectroscopy can offer vibrational information that is complementary to that obtained by IR. Furthermore, since the Raman spectrum reveals the backbone structure of a molecular entity [55], it is particularly useful in the examination of polymer film-coated electrodes. There are also some distinct advantages over in situ IR. For example, both the mid and far infrared spectral regions can be accessed with the same instrumental setup (in IR spectroscopy, these two regions typically require separate optics) [55]. Second, solvents such as water and acetonitrile are weak Raman scatterers thus the solvent medium does not optically obscure the electrode surface as it does in an in situ IR experiment. 

---