How it began
C. V. Raman, a professor at Calcutta University who was educated entirely in India, carried out his research at the Indian Association for the Cultivation of Science in Calcutta. On February 28, 1928 he and his student K. S. Krishnan discovered a previously unknown type of light scattering. Raman announced it to the press the same day and described it in a lecture to the South Indian Science Association in Bangalore on March 16, 1928. In the same year Grigory Landsberg and Leonid Mandelstam at Moscow State University independently observed the effect.
Before it existed
Raman had become absorbed in light scattering after showing that the color of the sea results from the scattering of sunlight by water molecules, the same argument Lord Rayleigh had used for the blue of the sky. His group in Calcutta then made an extensive series of measurements of light scattered mainly by liquids and also by some solids. The first observations of the new effect were made by eye, and precise measurements followed with a quartz spectrograph.
How it works
When a beam of colored light enters a liquid, a fraction of the light scattered by that liquid is of a different color. Raman showed that the nature of this scattered light depends on the type of sample present. The spectrum of Raman scattered light for any particular substance serves as a fingerprint that can be used to identify it, even in a mixture, and the intensity of the spectral lines is related to the amount of the substance. The technique applies to liquids, gases and solids.
What changed first
News of the discovery was reported by the Associated Press of India on February 29, 1928, and a thousand reprints of the paper were sent to scientists in different countries. Other scientists quickly understood the significance of the phenomenon as an analytical and research tool and called it the Raman effect. Raman was awarded the Nobel Prize in Physics in 1930.
What lasted
Raman spectroscopy later lost ground to infrared methods until the laser, which gave a far more intense light source, revived it in a new form beginning in the 1960s. India celebrates National Science Day every February 28 to commemorate the discovery. In 1998 the American Chemical Society and the Indian Association for the Cultivation of Science designated the discovery an International Historic Chemical Landmark.
