At the young age of 19, Raman already had a master’s degree in physics and had published his first research paper on the diffraction of light. His interest in optics and the scattering of light continued when he was observing the blue color of the Mediterranean Sea on his way to England in 1921. Using a simple Nicol prism, Raman concluded that water molecules scatter light just like air molecules do.
Following his observation, Raman focused on the principle behind this phenomenon by studying how light behaved when it passed through various substances. This led to the discovery that when light passes through a transparent material, a portion of it emerges at different angles from the initial direction, and some of this light is of different frequencies than that of the original light.
This phenomenon was called the ‘Raman effect’ and described the change in the wavelength of light that occurs when a light beam is deflected by molecules. For his work, Raman was awarded a Nobel Prize in 1930, making him the first Asian to be thus recognised in science.
What is Raman light scattering?
Raman is a light scattering technique, based on the interaction of light with the chemical bonds within a material, whereby a molecule scatters incident light from a high intensity laser light source. To best understand this, it’s easier to visualize light as particles or photons that can “bump into” or interact with the various molecules that may make up a sample of interest. Through this interaction, the photon changes the state of the molecule (rotationally or vibrationally) and the scattered photon shifts into a different state or energy.
For example, if the molecule ends up in a higher energy state than before, the scattered photon will be shifted to a lower frequency so that the total energy remains the same. Each molecule will have specific chemical bonds and symmetry that will produce distinct frequency changes, resulting in a Raman spectrum. A Raman spectrum features a number of peaks, corresponding to specific molecular bond vibrations, including individual bonds such as C-C, C=C, N-O, C-H, and groups of bonds such as benzene rings, polymers and lattices. |
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What is the Raman effect used for?
The Raman effect is now commonly utilised in spectroscopy to provide a structural fingerprint by which molecules can be identified. In a mixture of molecules, the Raman spectrum will contain peaks that correspond to each type of molecule. If the components are known, the relative peak intensities can be used to generate quantitative information about the mixture’s composition.
As the only requirement for this technique is for the sample to have chemical bonds, Raman spectra can be obtained for almost any material. Additionally, sampling is non-destructive and water, media, and buffers typically do not interfere with the analysis. Consequently, Raman spectroscopy has been used in a wide range of applications, from the identification of molecules in chemistry, to analysing nanomaterials, to imaging the distribution of macromolecules in bacteria using Raman microspectroscopy.
How has HORIBA pioneered the Raman effect?
When Raman first discovered this change in light frequency, he was using a mercury lamp and photographic plates to record spectra. This meant it could take hours or days to record spectra due to weak light sources and poor sensitivity. However, more than 30 years after the discovery of the Raman effect, lasers became commercially available and provided a much more powerful form of light source.
From then, HORIBA Scientific and its associated companies have been at the forefront of the development of Raman spectroscopy, with the first commercial Raman spectrometers unveiled in 1967. Raman microscopes followed in the 70s, and the first commercial Raman Laser microscope was developed in 1976 in France. Known as the MOLE™ (Molecular Optics Laser Examiner), this machine revolutionized the industry through its laser focus, but it was also the size of a room!
Subsequently, the technology has made rapid advancements in detection, filtering, imaging, and computing. One of the major breakthroughs was the development of Charge Coupled Devices (CCD) that enabled improved sensitivity and a much faster processing time. Now, HORIBA’s latest Raman product introduction, the LabRAM Soleil has set a new standard for Raman imaging and spectroscopy, delivering ultrafast imaging and advanced automation, all in a compact benchtop design.
If Raman was here today, he would surely be delighted to see how far his technique has come and how crucial it is now to scientific discovery. If you want to discover more about Raman spectroscopy, why not check out our comprehensive guide here?
