The Story of Raman Effect

By Dr Nandkumar M Kamat

February 28 has, since 1987, been celebrated as the National Science Day (NSD). The Raman Effect was discovered on that day in 1928. At the meeting of the Indian Academy of sciences at NIO last year, I bought a gem of a book – C V Raman - a pictorial biography compiled by S Ramaseshan and C Ramachandra Rao.

Ramaseshan mentions the events that led to the discovery of the Raman Effect. On his first voyage to Europe, Raman conducted an experiment on the ship to show that the blue of the Mediterranean Sea is due to molecular scattering and obtained the result that Rayleigh scattering must be a discontinuous process caused by photon collisions. From his intuition Raman had concluded that the interaction of the photon with a molecule must reveal itself by a change of colour. In an experiment done with K R Ramnathan, using sunlight filtered through a colour filter, "weak fluorescence’ was discovered.

Ramanathan thought that it was due to impurities. Raman saw the polarisation and rejected the impurity hypothesis. The seed of the Raman Effect was planted here, in 1925. Raman was so confident that he would discover a quantum effect in light scattering that when he needed funds to purchase a spectrograph he wrote to industrialist G D Birla. He wrote: "If I have it, I think I can get the Nobel Prize for India."

Raman resumed the work in December 1927 taking the benefit of the winter sun, in Calcutta. He persuaded his best student K S Krishnan to help him. Krishnan began the work on January 29-30, 1928. Both Raman and Krishnan worked tirelessly to detect the polarised "weak fluorescence" in all the liquids, gases and solids they examined.

Krishnan kept a diary in which he recorded: Tuesday 7 February 1928 - All pure liquids show fairly intense ‘fluorescence’…and what is more interesting, all of them are strongly polarised.

After the verification of these observations Krishnan wrote that Raman was much excited and repeated several times that it was an amazing result…one after the other, an entire series of liquids were examined and every one of them exhibited the phenomenon without exception. He wondered how we missed discovering all that five years ago writes Krishnan.

On February 9, 1928, Krishnan wrote in his diary: tried ether vapour and it was surprising that the modified radiation was conspicuous…professor came from the college at about three…and there was enough sunlight to see for himself.

What was the impact of this finding on Professor Raman?

Krishnan has captured the scene. He wrote: He ran about the place shouting all the time that it was a first rate discovery, that he was feeling miserable during the lecture because he had had to leave the experiment. He asked me to call everybody in the place to see the effect and immediately arranged in a most dramatic manner, with the mechanics, to make the arrangements for examining the vapours at high temperatures.

On February 28, Raman examined the scattered track with a direct vision spectroscope and found that the classical and modified scattering appear in the spectrum as separate region between them, a clear demonstration of a change of wavelength in scattering. They then used the mercury vapour lam and photographed the first ever Raman spectrum with a Hilger baby quartz spectrograph. Besides the incident radiation, several other lines were present in the scattered spectrum.

On March 16, 1928 Raman gave a lecture ‘A New Radiation’ in Bangalore and it was printed in the Indian Journal of Physics on March 31, 1928. Raman printed 3000 copies of the paper and posted these to the leading laboratories in the world.

On October 4, German physicist Sommerfel visited Raman’s laboratory. Sommerfeld wrote: "On October 6 saw the Raman Effect visually; heard a wonderful lecture by Raman. Saw the Raman Effect in ice, also that we can see rotation of molecules as ‘modified Radiation’."

Sommerfeld left the lab convinced about the Raman Effect and proposed Raman’s name for the Nobel Prize in Physics. Before leaving India Sommerfeld wrote, "India has suddenly emerged, in research, as an equal partner of her European and American sisters."

Besides Sommerfeld other well known scientists recommended Raman for the Nobel Prize for 1930. They were, Lord Rutherford, Neils Bohr, Louis de Broglie, Charles Fabry, Jean Perrin, Eugene Bloch, C T R Wilson and the Soviet scientist Chowlson.

On the eve of NSD 2011 it would be appropriate to conclude this article by mentioning what Professor Raman, a patriotic physicist, felt when he attended the Nobel Award ceremony as a citizen of British India and not an independent country. The American representative who was present for the ceremony described Raman’s emotional state: "Sir Venkata Raman, the Indian prize winner, upon returning to his seat on the platform after receiving his prize at the hand of King, was visibly moved by his emotion and sat with the tears streaming down his face."

Confirming this, Raman recalled, "When the Nobel Award was announced, I saw it as a personal triumph, an achievement for me and my collaborators – recognition for a very remarkable discovery, for reaching the goal I had pursued for 7 years. But when I sat in that crowded hall and I saw the sea of western faces surrounding me, and I, the only Indian, in my turban and closed coat, it dawned on me that I was really representing my people and my country. I felt truly humble when I received the prize from King Gustav; it was a moment of great emotion, but I could restrain myself. Then I turned around and saw the British Union jack under which I had been sitting and it was then I realised that my poor country, India, did not even have a flag of her own, and it was this that triggered off my complete breakdown."

About the famine of ideas in the Indian university system Raman remarked before his death on November 21, 1970, "Even a man of sensitivity and imagination can become bound and un-free when he has to falsify his feelings. If he forces himself to say that he likes what he dislikes and that he believes what he does not believe then he will have to pay the price in that his spontaneous and his creative faculties would dry up." But there are no more Ramans in India today because university system takes care to dry up creative faculties.