Grossary Glossary of Raman spectroscopy

Terms related to Raman scattering

Rayleigh scattering
When light is irradiated to a substance sufficiently smaller than the wavelength of light, scattering occurs on the surface. Of the generated scattering, the one with the same wavelength as the original light is called Rayleigh scattering.

Stokes Raman scattering, Anti-stokes Raman scattering
Both are Raman scattered light, which is a weak scattering with an intensity of about 10-6 as compared to Rayleigh scattering. Inelastic scattering accompanying the transition of electrons from the ground state to a high energy state by light irradiation is Stokes Raman scattering, and the reverse is anti-Stokes Raman scattering. In general, Stokes Raman scattering is stronger because electrons are more likely to be in the ground state, and it is common to use this for analysis.

Terms related to spectral performance

Spectral resolution (wavenumber resolution)
It is the wave number distance (horizontal axis) that can recognize two aligned Raman peaks as two independent peaks. Spectral resolution as a Raman spectroscopy system other than a spectrometer alone is evaluated by the full width at half maximum (FWHM) of a Rayleigh scattering peak when observing Rayleigh scattered light. Spectral resolution is determined by many factors, including the quality of the excitation laser (linewidth), the focal length of the spectrometer, the slit width of the spectrometer, and the type of grating.

Peak positioning accuracy
When measuring the shift amount of Raman peak by stress measurement etc., it is the peak positioning accuracy to decide how much shift amount can be detected. Fit the Raman peak with the Lorentz function etc. and calculate the peak position repeatedly to find its standard deviation. If the shift amount is larger than this standard deviation, it can be regarded as a significant peak shift, and the shift amount can be measured with higher precision than the wavenumber resolution.

Spectral pixel resolution
It is a value obtained by dividing the wavenumber range of the Raman spectrum by the number of pixels in the wave number direction of the detector. For example, if a spectrum in the range of 0 to 1000 cm-1 is detected by a CCD of 1000 pixels, the pixel resolution will be 1 cm-1 / pixel. Although this number is not wave number resolution, it should be noted that this number may be listed as wave number resolution because it is a product catalog.