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Raman spectroscopy is a technique to study the function of wavelengths between radiation and matter. Specifically, the science studies low-frequency modes such as vibrations and rotations. The main way the process works is by scattering monochromatic light without preserving the kinetic energy of the particles. When laser light interacts with the vibrations of structures within an atom, a reaction within the light itself is the result. This allows scientists to gather information about the system using Raman laser spectroscopy.
The basic theory behind Raman spectroscopy is the Raman effect. Light is projected onto a molecule with the intent of interacting with the electron cloud, the area around one or between electrons in an atom. This causes the molecule to become excited by individual units of light, known as a photon. The level of energy within the molecule is increased or decreased. Light from the particular location is then collected with a lens and relayed to a monochromator.
A monochromator is a device that optically transmits a narrow wavelength band of light. Due to the fact that bands of light scatter through transparent solids and liquids, known as Rayleigh scattering, the wavelengths closer to the light from the laser are dispersed, while the remaining light with the vibrational information is collected by a detector.
Adolf Smekal predicted the idea of the light scattering through the Raman effect in 1923. However, it wasn't until 1928 that Sir C.V. Raman discovered the possibilities behind Raman spectroscopy. His observations dealt primarily with sunlight due to the fact that laser technology was not readily available at the time. Using a photographic filter, he was able to project monochromatic light while observing that the light changed frequency. Raman was awarded the Nobel Prize in Physics for his discovery in 1930.
The most common uses for Raman spectroscopy is in the fields of chemistry, medicine and solid-state physics. Chemical bonds of molecules can be analyzed through the process, allowing researchers to more readily identify unknown compounds through the vibrational frequency. In medicine, Raman lasers can monitor the mixture of gases used in anaesthetics.
Solid-state physics utilizes the technology to measure the excitations of various solids. Advanced versions of the concept can also be used by law enforcement to identify counterfeit drugs while still in packaging. This occurs when the technology is limited in its sensitivity and allowed to essentially pass through certain layers until it reaches the desired molecule.