Raman spectroscopy anti-Stokes scattering

For any vibrational mode, the relative intensities of Stokes and anti-Stokes scattering depend only on the temperature. Measurement of this ratio can be used for temperature measurement, although this application is not commonly encountered in pharmaceutical or biomedical applications. Raman scattering based on rotational transitions in the gas phase and low energy (near-infrared) electronic transitions in condensed phases can also be observed. These forms of Raman scattering are sometimes used by physical chemists. However, as a practical matter, to most scientists, Raman spectroscopy means and will continue to mean vibrational Raman spectroscopy. 

Inverse Raman spectroscopy The Inverse Raman effect is a form of Raman scattering, first noted by W.J. Jones and B.P. Stoicheff, wherein stokes scattering can exceed anti-Stokes scattering resulting in an absorption line (a dip in intensity) at the sum of irradiated monochromatic light and Raman frequency of the material. This phenomenon is referred to as the inverse Raman Effect, application of the phenomenon is referred to as inverse Raman spectroscopy, and a record of the continuum is referred to as an inverse Raman spectrum. 

Among the advanced techniques employed to follow the cure reaction, Fiber Optic Raman Spectroscopy has been an effective tool. By this technique, both the temperature build-up and the cure advancement of AroCy L-10 could simultaneously be followed. The local temperature of the sample, determined by Ra-man-Stokes and anti-Stokes scattering of a reference peak correlated well with the temperature measured using a thermocouple probe. The extent of cure could be monitored using either individual peaks associated with the reactant or product or by using the entire spectrum [104]. 

Raman spectroscopy (RS) is a well known technique to detect the vibrational characteristics of molecules in various media and is therefore extensively used in physics chemistry and biologyGenerally this technique is easily implemented, and does not require sample preparation. In addition RS has the advantage that it can be applied in water solutions, in contrast to IR absorption. In a classical picture RS results from the inelastic interaction between a molecular system and the electromagnetic field of a laser source." The electronic polarizability is modulated by the vibration mode associated with the motion of the molecule, at a frequency (Raman shift) which is the difference (Stokes scattering) or the sum (anti-Stokes scattering) between the laser and the molecular frequencies. The induced dipole moment can be written as ... 

Vibrational excitations can be created, which causes a decrease in the frequency (i.e., in energy) of the scattered light, or they can be amiihilated, which causes an increase. The decrease in frequency is called Stokes scattering and the increase is anti-Stokes scattering. Stokes scattering is the normal Raman effect and Raman spectroscopy generally uses Stokes radiation. 

Another potential development in fiber analysis techniques has been the use of Raman spectroscopy for dye analysis. Electromagnetic radiation can interact with molecules so that it can be reflected, absorbed, or scattered. The light that is scattered can either be more energetic than the incident light, in which case it is called Stokes scattering, or of a lower energy, i.e., anti-Stokes scattering. This effect is called the Raman effect and is named after C.V. Raman, who was the first to observe this effect. 

Stokes-shifted from the incident frequency coi, anti-Stokes scattering is obtained when o)i < 0)2- The energy difference h(co2 — ( i) normally matches either a molecular vibrational-rotational or rotational level difference, and the incident frequency cOi is usually some readily generated visible frequency (e.g., an Ar" or He/Ne laser line) in conventional Raman spectroscopy. In such cases c 2 — 1- We may specialize Eq. 10.26 to chemical applications of... 

Depending on the relative phase difference between these temis, one may observe various experimental spectra, as illustrated in figure Bl.5.14. This type of behaviour, while potentially a source of confiision, is familiar for other types of nonlinear spectroscopy, such as CARS (coherent anti-Stokes Raman scattering) [30. 31] and can be readily incorporated mto modelling of measured spectral features. 

Coherent anti-Stokes Raman scattering spectroscopy... 

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