“I propose this evening to speak to you on a new kind of radiation or light emission from atoms and molecules.” With this sentence,Dr. C.V. Raman began his historic lecture in Bangalore on March 16, 1928. Dr. Raman would go on to introduce the Raman Effect, a phenomenon that changed the study of light scattering for many years to come.
Sir Chandrasekhara Venkata Raman was born in the Madras Presidency of India in 1888. Dr. Raman, whose speciality had been the study of vibrations and sounds of stringed instruments like the violin, veena and tambura, and also percussion instruments like the tabla, was returning from a sojourn to London on a 15-day sea voyage. While observing the deep blue colour of the Mediterranean sea, his mind was unable to accept that the colour of the sea was simply a reflection of the sky. This led him to later show through multiple experiments that the colour of the sea was, in fact, the result of the scattering of sunlight by the molecules of water, similar to the explanation of the blue colour of the sky.
Later, upon further experiments, Dr. Raman and his team were able to show that some of the scattered light was actually of a different colour than the incident beam entering the scattering medium. This they found by using a violet filter on white light to pass only violet light into water (scattering medium). Upon studying the scattered violet light, Dr. Raman and his team found traces of green light (which is of a different wavelength) while using different filters. This led Dr. Raman to coin the Raman Effect, which states that when a light beam is deflected by molecules in a scattering medium, a change in the wavelength of the light can also occur. The Raman Effect is a very weak effect. To put this in perspective, approximately only 1 photon out of 1,000,000 would undergo this change. How does the Raman Effect take place? The change in wavelength can be attributed to the transfer of energy from the photons of the incident beam to the molecules of the scattering substance.
His discovery not only gave further proof of the quantum theory of light and contributed to the field of physics but also found applications in chemistry and forensics for non-destructive analysis of chemical substances. The unique spectrum of the scattered light from any material was like a fingerprint and could be used for analysis of mixtures. It could be used for liquids, gases and solids. The development of the laser in the 1960’s further enhanced Dr. Raman’s spectroscopic methods.
In his lecture, Dr. Raman concluded by saying “We are obviously only at the fringe of a fascinating new region of experimental research which promises to throw light on diverse problems…”
Regarded as one of the greatest scientific minds the world has ever seen, Dr. Raman was the first Asian to earn the Nobel Prize in Physics. Dr. Raman’s avant-garde work in the field of light scattering also earned him a knighthood and the Bharat Ratna.