In 1986, the Government of India, under then Prime Minister Rajiv Gandhi, designated February 28 as National Science Day to commemorate the announcement of the discovery of the “Raman Effect”. This year’s edition is being celebrated under the theme of “Global Science for Global Wellbeing”, in light of India’s G20 presidency.
The Raman Effect was the discovery which won physicist Sir CV Raman his Nobel Prize in 1930. Conducting a deceptively simple experiment, Raman discovered that when a stream of light passes through a liquid, a fraction of the light scattered by the liquid is of a different colour. This discovery was immediately recognised as groundbreaking in the scientific community, being the subject of over 700 papers in the first seven years after its announcement.
What is the “Raman Effect”? Why is it so important? Most importantly, who was the man behind this momentous discovery?
A young prodigy conducting after-hours research
Raman was born to a family of Sanskrit scholars in Trichy (present-day Tiruchirapalli) in the Madras Presidency in 1888. At the age of only 16, He received a BA degree from Presidency College in Madras, and was placed first in his class. While studying for his MA degree, at the age of 18, he got published in the Philosophical Magazine: this was the first research paper ever published by Presidency College.
Due to his ill health, he was unable to travel abroad for further education. Thus, in 1907, he got married and settled down in Calcutta as an assistant accountant general. While still a full-time civil servant, Raman began after-hours research at the Indian Association for the Cultivation of Science (IACS). Raman raised the profile of IACS, doing some award-winning research as well as conducting public demonstrations with charisma. At the age of 29, he finally resigned from his civil services job and took up a professorship in Presidency College, Calcutta.
A voyage across the ocean leads to interest in the scattering of light
By 1921, CV Raman had gained a solid reputation as a top scientific mind both in India and in the West. That year, he made his first journey to England. It was on the return journey that Raman would make an observation that would change his life and science forever.
While passing through the Mediterranean Sea, Raman was most fascinated by the sea’s deep blue colour. Dissatisfied with the then-accepted answer (“the colour of the sea was just a reflection of the colour of the sky”), his curious mind delved deeper.
He soon found out that the colour of the sea was the result of the scattering of sunlight by the water molecules. Fascinated by the phenomenon of light-scattering, Raman and his collaborators in Calcutta began to conduct extensive scientific experiments on the matter – experiments that would eventually lead to his eponymous discovery.
Simply put, the Raman Effect refers to the phenomenon in which when a stream of light passes through a liquid, a fraction of the light scattered by the liquid is of a different colour. This happens due to the change in the wavelength of light that occurs when a light beam is deflected by molecules.
In general, when light interacts with an object, it can either be reflected, refracted or transmitted. One of the things that scientists look at when light is scattered is if the particle it interacts with is able to change its energy. The Raman Effect is when the change in the energy of the light is affected by the vibrations of the molecule or material under observation, leading to a change in its wavelength.
In their first report to Nature, titled “A New Type of Secondary Radiation,” CV Raman and co-author KS Krishnan wrote that 60 different liquids had been studied, and all showed the same result – a tiny fraction of scattered light had a different colour than the incident light. “It is thus,” Raman said, “a phenomenon whose universal nature has to be recognised.”
Raman would go on to verify these observations using a spectroscope, publishing the quantitative findings in the Indian Journal of Physics on March 31, 1928.
The importance of the discovery
CV Raman’s discovery took the world by storm as it had deep implications far beyond Raman’s original intentions. As Raman himself remarked in his 1930 Nobel Prize speech, “The character of the scattered radiations enables us to obtain an insight into the ultimate structure of the scattering substance.” For quantum theory, in vogue in the scientific world at the time, Raman’s discovery was crucial. The discovery would also find its use in chemistry, giving birth to a new field known as Raman spectroscopy as a basic analytical tool to conduct nondestructive chemical analysis for both organic and inorganic compounds. With the invention of lasers and the capabilities to concentrate much stronger beams of light, the uses of Raman spectroscopy have only ballooned over time.
Today, this method has a wide variety of applications, from studying art and other objects of cultural importance in a non-invasive fashion to finding drugs hidden inside luggage at customs.
Source: Indian Express, 28/02/23
