Raman spectroscopy radiation sources

Lasers (see Chapter 9) are sources of intense, monochromatic radiation which are ideal for Raman spectroscopy and have entirely replaced atomic emission sources. They are more convenient to use, have higher intensity and are more highly monochromatic for example, the line width at half-intensity of 632.8 nm (red) radiation from a helium-neon laser can be less than 0.05 cm. ... 

Another technique of vibrational spectroscopy suited for the characterization of solids is that of Raman spectroscopy. In this methodology, the sample is irradiated with monochromatic laser radiation, and the inelastic scattering of the source energy is used to obtain a vibrational spectrum of the analyte [20]. Since... 

The use of an Intense laser light source with biological materials Is accompanied by the concomitant problems of localized sample heating and the possibility of protein denaturetlon. A further complication Introduced by resonance Raman spectroscopy Is the Increased potential for photochemical destruction of chromo-phorlc metal centers as a result of the absorption of large amounts of Incident radiation. Both of these situations may be ameliorated by freezing samples to liquid nitrogen temperature ( 90 K), while the even lower temperatures made possible with a closed-cycle... 

In surface-enhanced Raman spectroscopy (SERS) samples are adsorbed onto microscopically roughened metal surfaces. Spectra are the intensities and frequencies of scattered radiation originating from a sample that has been irradiated with a monochromatic source such as a laser. SERS spectra are of molecules that are less than 50 A from the surface. 

The amount of radiation used is also important. A Nernst glower is used in ordinary infrared spectroscopy. This light source emits a relatively low amount of radiation, and no destruction of the analyzed material occurs. However, Raman infrared spectroscopy employs a radiation source of much greater energy. This radiation is sufficiently energetic to cause bond disruption and some destruction of the analyzed material. 

He/Ne laser focussed into a small tapered hole in a pellet of the plastic. The flux density achieved at the focus was about 1000 Watts/cma. The scattered radiation was examined using a double spectrometer and photon-counting detection. A very fine spectrum, superior even to that of Maklakov and Nikitin (see Table 1), was recorded photo-electrically. Schaufele pointed out that a band atAv= 109cm-1 forecast previously by Tadokoro et aL (15) was not observed at first but in a note added in proof he mentions that a feature may be genuine at 98 2 cm-1. A band had already been observed at Av= 110cm-1 by instrument developers at the Cary Instrument Co. since Szymanski (16) shows a spectrum of isotactic polypropylene, recorded at Monrovia, Calif., on a laser sourced Cary 81 spectrometer, as an example of recent advances in Raman spectroscopy. 

The application of classical Raman spectroscopy, using the mercury radiation at A 253.6 nm as the excitation source, permitted recording20 of more than 20 peaks for sucrose below 500 cm-1. The observed frequencies below 100 cm"1 were interpreted as due to inter-ring oscillations, which was also the conclusion reached from a far-infrared study84 of glucose and sucrose. 

In this article, we would like to point out that time re -solved resonance Raman spectroscopy (TRRR) Is a powerful tool which, with the use of lasers as radiation sources and vidlcon... 

All other types of birefringent polarizers listed above exploit the same physical principle and differ only in their construction. Immersion media are more often used instead of the air gap in order to achieve a rigid device. Birefringent polarizers are mainly used in Raman spectroscopy for polarization of the radiation of a laser light source. 

In vibrational spectroscopy, usually classical (thermal) radiation sources are employed to measure absorption in the NIR, MIR, and FIR range, however, lasers will be used increasingly depending on the progress of development. Lasers are used nearly exclusively for Raman spectroscopy. 

Interferometric Raman spectroscopy Interferometric Raman Spectroscopy is a measurement technique that utilizes time-domain or space-domain measurements of electromagnetic radiation or other type of radiation for collecting Raman spectra based on the coherence of a radiative source. An example is a Fourier transform (FT) Raman spectrometer. 

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