This National Science Day, let the scattered light shine on C V Raman and his Raman effect

Ronak Gupta February 28, 2017 8 min

Great discoveries in science are often accompanied by stories that themselves become legends, whether they be true or false. The discovery of gravity is usually associated with the image of Newton sitting under an apple tree, and concepts of flotation and buoyancy conjure the image of a butt-naked Archimedes exclaiming “Eureka”.

There are, however, many groundbreaking discoveries that come from stories not quite as dramatic as these. C V Raman’s (1888-1970) discovery of the eponymous effect of light scattering in liquids is one such discovery.

For once, let’s celebrate this day, and the greatest achievement of one of India’s greatest citizens — C V Raman and his discovery of the Raman effect  

Among the sea of hyper-commercialised ‘days’ that we celebrate in our country, National Science Day makes a ton of sense. For once, let’s celebrate this day, and the greatest achievement of one of India’s greatest citizens — C V Raman and his discovery of the Raman effect.

Why is the sea blue?

Here’s a little story to pique your interest.

In 1921, during a voyage back from England after meeting JJ Thompson and John Rutherford — luminaries of science at that time — Raman wondered why the sea was blue. The prevailing explanation was that the water reflected the sky and looked blue because the wavelength of light that was most efficiently scattered by the molecules in the sky made up the blue spectrum.

Raman, however, pondered over the matter, and carried out some elementary experiments onboard that convinced him that water looks blue for pretty much the same reason the sky looks blue, not because of the the sky. Raman wrote to Nature, a premier science journal, on his arrival in India. His letter bears the address not of his home or research laboratory, but of the harbour at which the ship was docked — a glimpse of Raman’s intense dedication to science.

C V Raman’s discovery of the eponymous effect of light scattering in liquids may not be associated with a story quite as dramatic as Newton’s discovery of gravity — the image of Newton sitting under an apple tree — but it was groundbreaking  

It is likely that these elementary studies pushed Raman towards further investigating the phenomena of scattering of light by liquids. Back in his office at the Indian Institute of Cultivation of Science in Kolkata, he embarked on this research in a systematic manner.

The Raman effect

Bear in mind, this was mid-1920’s and India, firmly under British rule, was hardly a conducive place for research. Undeterred, Raman carried out simple but careful experiments, which were the first to show that light passing through liquids, solids even, can come out of them with a different wavelength. Only someone with hawk-like curiosity and observation could have made this discovery, because this anomalous scattering effect has existed in nature forever, but was so minimal that it escaped detection.

Most of the light that passes through a material emerges without any change in its wavelength. This scattered light, dubbed as ‘Rayleigh scattering’, is a common phenomena and is responsible for the blue colour of the sky among other things.
Let’s break down this effect to better understand it. Imagine light is made up of (and it is) particles called photon that carry energy. These photons when sent through a medium, collide with medium molecules, and emerge without any change in energy. These collisions are elastic in nature, and as such dont result in either the medium molecule or the hitting photon to gain or lose energy. But, some of these interactions exchange energy. And these rogue collisions result in the emerging photons of light with either reduced or gained energy — producing a scattered light profile which is now called the Raman effect.

Raman carried out simple but careful experiments, which were the first to show that light passing through liquids, solids even, can come out of them with a different wavelength

Since the number of such rogue collisions is low, the higher the concentration of molecules, the more enhanced the Raman effect, which explains why the effect is minimal in gases with low concentrations. Raman worked with liquids, which are denser than gases, and hence more prone to show these effects, and in 1928, submitted a report first to the Indian Journal of Physics and then to Nature — a journal synonymous with publishing many of the groundbreaking discoveries that have lead to Nobel Prizes.

Gathering scattered light to decipher material make-up

What Raman and his coworkers discovered is essentially a new kind of radiation — a signature that can be used for identifying materials, much like a fingerprint analysis. When a photon interacts with a molecule — a rogue collision, a molecule can use some of the energy of the photon, accessing a “mode” with higher energy. The loss of energy for the photon manifests as a change in wavelength, which is seen in the scattered light.

Sometimes, a photon may gain energy instead and this too manifests as a change in wavelength. Here’s the method in full glory: You shine a source of light that passes through a test material, and you collect the scattered light at the other end. Some of the scattered light would be of a different wavelength, and so a different colour. Depending on the specific material used — gas, liquid, solution or a mixture — the scattered light will show varying patterns, bands of different colour, and peaks at different wavelengths.

The Raman effect has been used for a variety of analyses — ranging from decoding what lunar soil is made up of to analysing nuclear materials and industrial effluents  

The Raman effect thus became a powerful tool for identifying material makeup and structure. It has been used for a variety of analyses — ranging from decoding what lunar soil is made up of, to analysing nuclear materials and industrial effluents. This practice of finding out what elements make up a certain material by using the principle of the Raman effect is dubbed Raman spectroscopy. What makes it such a powerful tool is that it’s not only easy to implement and understand, but also non-invasive.

Also, the tool has aged well. Lasers allows for a directed intense beam of light that leads to an enhanced spectra and clearer effects. Modern computers and data-handling tools have made Raman spectrography commonplace. From being a strong proof, yet again for the quantum nature of light to being a chemists standard tool, to becoming one of the first lines of attack for a materials scientist, the Raman effect was a momentous discovery then and is a bedrock of experimental physics now.
And it was first discovered, not by the guys in England who discovered the electron and nucleus, or the famed Copenhagen group — the fathers of quantum mechanics, but by a turbaned scientist in British-ruled India driven by curiosity.

A man of science

Raman’s utmost devotion to science is legendary. He was a man who marvelled at the vagaries of nature and natural laws as much as he was possessed by a curious and meticulous nature, characteristic of experimentalists.

T S Satyan, a famous photojournalist recalls his time spent with Raman vividly, sharing more than one anecdote about him in his autobiography, Alive and Kicking. In one incident, Satyan talks about how one of his associates ended up breaking his camera, causing Raman to be livid; he, however, cooled down quickly and scribbled these words on a piece of paper: “Prisms out of alignment. Replace one broken piece and realign. Set right the metallic dents.”

He was a man who marvelled at the vagaries of nature and natural laws as much as he was possessed by a curious and meticulous nature, characteristic of experimentalists  

I haven’t had the good fortune of attending a lecture by Raman, but many have cited his exemplary oratory skills and talks peppered with live physics demonstrations. I have, however, had the good fortune of going through some of Raman’s research letters, and there is no doubt that he was a brilliant writer. Often, technical writing in science is dense and impenetrable, with even scientific repartee filled with jargon. Raman’s papers are clear, cogent and easy to understand.

Beyond science, his lasting achievement was trying to setup a foundation for physics research in independent India, at a time when research was in its absolute nascency. Raman established the department of physics at the Indian Institute of Science in Bengaluru (IISc), which, for the longest time was the centre of research in India and, as some would argue, still is. After retiring from IISc in 1948, he founded the Raman Research Institute (RRI) in Bengaluru, which now conducts cutting-edge research in a variety of fields.

Why did Raman never become an icon of science, like Albert Einstein did, in his own country even, and why do crowds not flock to his bungalow in Malleshwaram  

As a young engineering student, I was always fascinated by physics. I devoured biographies of great physicists, forever quoting Richard Feynman, idolising the singular genius of Albert Einstein and marvelling at how Newton did what he did.

But, I never read about Raman’s work, never picked up any book about him, or read about him in any pop culture reference. I wonder why. Why did Raman never become an icon of science, like Albert Einstein did, in his own country even, and why do crowds not flock to his bungalow in Malleshwaram as this piece in The Hindu reported.

Maybe he has somewhat faded from public memory. We in India, often let that happen with heroes and Raman wasn’t any hero, he was a scientist. As I write this piece, I am constantly reminded about how lucky I am to go to work everyday at a place where Raman laid down the groundwork for Indian research. Maybe I’ll pause at a bust of his in the foyer and ponder about it again.

Lead visual: Nikhil Raj