Great Scientists and their Inventions
C. V. Raman( 1888-1970)
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C. V. Raman discovered that when light interacts with a molecule the light can donate a small amount of energy to the molecule. As a result of this, the light changes its colour and the molecule vibrates. The change of colour can act as a ‘fingerprint’ for the molecule.
Today Raman spectroscopy, which relies on these ‘fingerprints,’ is used in laboratories all over the world to identify molecules and to analyze living cells and tissues to detect diseases such as cancer.
Raman and Rayleigh Scattering
Lord Rayleigh, who had believed the teenage Raman’s papers were the work of a professor, had been one of the great physicists of his day. He had won the 1904 Nobel Prize in Physics.
His importance to Raman’s story is that Rayleigh had been the first to explain why the sky is blue. He had then explained the sea’s color by saying it was simply a reflection of the sky’s color.
One day, in the summer of 1921, Raman was on the deck of a ship in the Mediterranean Sea en route to the Congress of Universities of the British Empire at Oxford. He looked at the beautiful blue color of the Mediterranean Sea and began to doubt Rayleigh’s explanation of its color.
Rayleigh had correctly explained that the sky looks blue because of a phenomenon now called Rayleigh scattering.
If Earth had no atmosphere, anyone who happened to be around in such circumstances would see a white sun and a black sky. However, this is not what we see, because sunlight interacts with the gases in Earth’s atmosphere.
Rather than coming straight to our eyes from the sun, sunlight is scattered in all directions by the atmosphere. Blue light is scattered most, meaning that it comes to our eyes from everywhere in the sky, therefore the sky looks blue. Yellow and red light are scattered least, so we usually see a yellow sun, and sometimes a red sun.
Rayleigh scattering is elastic. This means that photons of light lose no energy when they interact with gas molecules. The light, therefore, stays the same color.
Raman Discovers that the Sea Scatters Light
When he sailed back to India in September 1921 Raman, an indefatigable scientist, had with him some simple physics apparatus: a prism, a miniature spectroscope, and a diffraction grating. He used these to study the sky and the sea and concluded that the sea was scattering light.
Hence when Rayleigh said the sea’s color is simply a reflection of the sky’s color, he was not wholly correct. Raman reported his findings in a letter to the journalNature.
When he returned to his laboratory, Raman and his students began an exhaustive program of research into light scattering.
The Raman Effect
Raman and his students continued researching light scattering in gases, liquids and solids.
They used monochromatic light – sunlight that had been filtered to leave only a single color – and found that a variety of different liquids – sixty of them – did indeed change the color of the light. They first observed this in April 1923, but very weakly.
In 1927 they found a particularly strong color change in light scattered by glycerol (then called glycerine):
Raman is the highly interesting result that the colour of sunlight scattered in a highly purified sample of glycerine was a brilliant green instead of the usual blue.”
C. V. RAMAN: PHYSICIST
Nobel Lecture, 1930
Raman’s team observed the effect in gases, crystals and glass. The effect might have been mistaken for fluorescence, another phenomenon in which light has its color changed, but in Raman’s work the light scattered by liquids was polarized, which ruled out fluorescence.
What came to be known as the Raman effect – a color change accompanied by polarization – had never been seen before. The inelastic scattering at its heart was a further, very strong confirmation, of quantum theory.
Approximate Representation of the Raman Effect
The Raman effect is a very small effect compared with Rayleigh scattering. Only about 1 in ten million photons undergoes inelastic scattering.
Raman and his colleague K.S. Krishnan reported their discovery in March 1928 in Nature.
Raman was awarded the 1930 Nobel Prize in Physics for “work on the scattering of light and for the discovery of the effect named after him.”
Raman showed that the energy of photons scattered inelastically serves as a ‘fingerprint’ for the substance the light is scattered from. As a result of this, Raman spectroscopy is now commonly used in chemical laboratories all over the world to identify substances. It is also used in medicine to investigate living cells and tissues – even detecting cancers – without causing harm. Laser light rather than sunlight is used as the source of photons.
The Photon’s Spin
In 1932 Raman and his student Suri Bhagavantam discovered that photons of light carry angular momentum – in quantum terms, photons possess a property called spin.
Light and other forms of electromagnetic radiation pass their angular momentum on to atoms that absorb them.
In 1933 Raman became the first Indian director of the Indian Institute of Science in Bangalore. In 1947 he became independent India’s first National Professor. In 1948 he founded the Raman Research Institute in Bangalore, where he worked until the end of his life.
He was suspicious of governments playing any role in fundamental science, refusing government funding for his work:
Chandrasekhara Venkata Raman died, aged 82, of heart disease on November 21, 1970 in Bangalore, India
Not get afraid of asking questions. Ask the right questions and nature will open the doors to her secrets.
I am the master of my failure… If I never fail how will I ever learn?
Real growth of a country was in hearth, mind, bodies and souls of young men and women of the country.