Raman spectroscopy—how does it work?

In 1930, Indian physicist Sir Chandrasekhara Venkata Raman received the Nobel Prize in Physics for detecting the Raman effect, which is named after him: If light strikes atoms or molecules, photons and molecules interact. The energy level of these photons drops, which changes their wavelength. With the spectra of this scattering, which is clearly and measurably different from the incident light, it is possible to precisely determine the scattering molecule. Due to the different molecular mass, atomic bond and the resulting differences in vibration and rotation, each molecule triggers a characteristic scatter signal: the spectroscopic “fingerprint” of the molecules. Consequently, Raman spectroscopy can also identify complex bio-molecules unequivocally.

By comparing results with the respective databases, Raman spectroscopy can be used to determine the molecular composition of solid, liquid, and gaseous substances quickly and extremely accurately. This is why the method is used extensively. Potential applications include the chemical and pharmaceutical industries, research, life sciences, and material sciences.

In Raman spectroscopy, excitation is carried out with lasers with as narrow a spectral range as possible. According to Coherent, the most commonly used are continuous wave (cw) lasers with wavelengths from 488 Nanometer (nm), 532 nm, 631 nm, and 750 nm; in some cases, also UV lasers in the wavelength range below 270 nm. There are also other methods, such as Coherent Anti-stokes Raman Spectroscopy (CARS), which uses ultrashort pulse lasers rather than cw laser beam sources.

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