Spectroscopy: Raman Methods

General Raman
The most common application of Raman spectroscopy involves the vibrational energy levels of a molecule. Incident laser light in the UV, visible or NIR, is scattered from molecular vibrational modes.

Tip-Enhanced Raman Spectroscopy
TERS - Tip-Enhanced Raman spectroscopy

Surface-Enhanced Raman Spectroscopy
SERS - Surface-enhanced Raman spectroscopy

Coherent Anti-Stokes Raman Spectroscopy
Coherent Anti-Stokes Raman spectroscopy (CARS) a type of non-linear Raman spectroscopy. Instead of the traditional single laser, two very strong collinear lasers irradiate a sample.

Resonance Raman Spectroscopy
Instead of fluorescence, some types of colored molecules produce strong Raman scattering at certain conditions. This effect was called Resonance Raman.

Stimulated Raman Scattering
Stimulated Raman scattering takes place when an excess of Stokes photons that were previously generated by normal Raman scattering are present or are deliberately added to the excitation beam.

The Raman Effect

The Raman effect is a light scattering phenomenon. Photons incident on a molecule or crystalline solid may be scattered elastically, termed Rayleigh scattering, or inelastically through the exchange of energy with vibrational states, termed Raman scattering. In all forms of inelastic scattering, the energy, and hence the wavelength of the incident and scattered photons are not equal. However, energy is always conserved, and so the energy of the molecule must change to make up the deficit. Energy levels are quantized, so Raman scattering occurs only at discrete wavelengths corresponding to transitions between vibrational energy levels. The set of wavelengths resulting from Raman scattering of monochromatic incident light is termed the Raman spectrum, and analysis of these wavelengths is known as Raman spectroscopy.

Raman spectroscopy
Figure 1: Rayleigh scattering, Stokes scattering and anti-Stokes scattering


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