Around nine decades ago, a young man called Chandrasekhara Venkata Raman from the town of Tiruchirappalli in Tamil Nadu was sailing back to India after attending a conference in London. Raman was already a physicist of repute at the University of Calcutta. As the story goes, during the voyage, Raman would often sit on the ship’s deck and gaze at the azure of the Mediterranean Sea. Eventually, and perhaps inevitably, given his interest in the study of light, Raman began to wonder where the sea got its colour from.
The prevailing notion at the time was that the blue of the sea was a reflection of the sky. As for the sky’s colour, physicist Lord Rayleigh had won a Nobel Prize in 1904 for proposing that it was due to minute particles in the air scattering the blue wavelength from the sun’s white rays, while absorbing all other wavelengths of colour. But Raman had a hunch that the sea’s hue was more than just a reflection of the sky. Using a Nicol prism, he eliminated some of the light from the sky that the sea reflected. This made the water’s colour grow even more intense. “The hue of the water is of such fullness and saturation that the bluest sky in comparison with it seems a dull grey,” Raman wrote in an article in the journal Nature in 1921, describing his observations with the Nicol prism. Clearly, water was responsible for its own colour, rather than merely reflecting the sky’s.
Over the next seven years, Raman and his students—including physicist KS Krishnan—shone light onto several transparent liquids, ranging from water to glycerine. Each time, they saw a faint glow: Blue in the case of water, green in the case of glycerine and so forth. Finally, on February 28, 1928, celebrated as Indian Science Day, Raman described to a group of scientists in Bangalore the phenomenon that would win him India’s first Nobel for science. Although Krishnan contributed greatly to the discovery as a co-discoverer of the Raman Effect—and for which he is widely acknowledged—he didn’t share the Nobel.
Raman Scattering or Raman Effect—as the phenomenon was eventually named—is the scattering of light that falls on a substance, leading to a change in the colour of the light that emerges from the substance. Normally, a large part of incident light gets absorbed, transmitted or reflected. But a tiny part—about one out of every 10,000 photons (light particles) that fall on a substance—undergoes Rayleigh scattering. This means the photon gets scattered, but doesn’t change its wavelength and, therefore, its colour. An even tinier part—about one photon in 10 million—not only scatters, but also changes its wavelength and colour. What’s more, the change in the colour of the light is decided by the substance that scatters the light. When the substance is water, for example, the light turns blue. By studying the altered light, therefore, one can identify the substance as water.
Raman spectroscopy, which uses this phenomenon to detect various substances, is today used in everything from quality control in the pharmaceutical industry (examining active pharmaceutical ingredients in drugs) to medical diagnostics like understanding the composition of tumours in cancer patients. Physicists continue to tweak this powerful technique while being on the constant look out for new applications, and new ways of observing the Raman Effect closely. Hundreds of papers are written each year, several of them by Indian scientists.
Joining the ranks this year are two groups of scientists, one from the Indian Institute of Science (IISc) in Bangalore, and the other from the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) in Bangalore and the University of Mysore. While IISc researchers showed how Raman spectroscopy can identify dangerous substances such as improvised explosive devices (IEDs) at airports and border checks, scientists from JNCASR and the University of Mysore showed how it can help drug discovery. Both methods shine new light on the problems of imaging opaque substances and screening compounds that hold the potential to form new drugs.
Sil and Umapathy have some way to go before their method is ready for the field, say other researchers. Sudipta Maiti, an expert in imaging technologies at Mumbai’s Tata Institute of Fundamental Research, says that while Sil’s and Umapathy’s research is interesting, t-Stilbene, the compound used in their experiment, is a “good Raman emitter”; because it is a dye, t-Stilbene’s Raman spectra is strong and easily detectable. The real test for UMARS would be if the experiment was reversed, and ammonium nitrate was placed in the inner ampule; ammonium nitrate has a weaker Raman spectra and would be more difficult to detect. “Several other substances you may want to detect may or may not be good Raman emitters,” Maiti says. “In that case, it becomes a problem for this method. More work needs to be done by the researchers to overcome this.”
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(This story appears in the 05 September, 2014 issue of Forbes India. To visit our Archives, click here.)
Congratulations.... from bottom of my heart.... your article halped me in my seminor.... another thing is you pepole made Indians to feel proved by reserching on the topic which proved by lndian scientist... wish u all good luck for your further reserches.....on Oct 13, 2014
My Dear student ( 2 level) Sanchita, I am very glad to read this article for your new discovery. I am also working on Raman specroscopy since last 14 years and I hope we may work together in near future based on Raman spectroscopy. With all the best!! Your School-Physics Teacheron Sep 4, 2014
Thank you so much Sir! Would love to work with you.You must visit our lab at IISc and meet my supervisor Prof Umapathy. Yours sincerely Sanchitaon Sep 4, 2014
Thank you for this wonderful article. In my schooldays it was told that Ramans research though of no practical utility,may be of some use someday ! That of course was a very long time ago.on Aug 28, 2014