The Raman Effect

Last year I went on a trip to Rameshwaram, which is an island in the south of India. It is a very important pilgrimage center, famous for an ancient Shiva temple believed to have been built by Lord Rama. We had to get to the town via a bridge built across the ocean. The sea looked so beautiful from there. I have never seen so many colors in the ocean. It varied from Aquamarine green to deep blue.

It reminded me of the great Indian scientist Sir C.V.Raman who got the inspiration for his Nobel Prize winning theory as he observed the deep blue of Mediterranean Sea from the deck of his ship. I thought I should write about him.  

Before Raman propounded his theory it was believed that the sea was blue because it reflected the blue of the sky. Raman observed that the Mediterranean appeared blue even when the sky was dull gray. After extensive research in his laboratory in India he found that the color of the sea changes because of a phenomenon called inelastic scattering of light. Why is the sky blue? Because it scatters the blue light more than any other wavelength. A similar phenomenon occurs in ocean. However in addition to scattering the light , the molecules of the water absorb some energy from the light. A lower energy light radiation is emitted and thus color of the sea changes. It is not identical to the color of the sky. It can easily be understood through quantum theory. Photons of higher energy are absorbed and lower energy are released by the molecules. If you look at the picture above, the color varies directly proportional to the depth of the sea. I think it is because, in deeper areas of the sea there are more water molecules and hence more energy loss and those areas appear green (green is of lower frequency and hence lower energy photons)whereas the in the shallower regions the energy loss in less hence it is blue.  

Raman also found that this loss of energy or shift in wavelength is dependant on the medium. Hence it was possible to study the molecules of the medium and the structural arrangement by passing light through it. Raman won the Nobel prize in physics for his finding. Today, Raman Effect is considered to be one of the four major discoveries in experimental physics of the early twentieth century.  

What is even more commendable about his finding is that it happened in his laboratory in India. He did not have sophisticated instruments or technology which was available to the western scientist of his times. In fact he did not have the money to buy a light source, so conducted his experiments using sunlight. He is believed to have said “The essence of science is independent thinking and hard work, not equipment” 

Till he died, Raman continued to do research, give talks and inspire students. During his life he wrote 360 research papers and four books. He founded schools of physics in Kolkata and Bangalore. To mark the anniversary of the discovery of Raman effect, Feb 28^th  is celebrated as “National Science Day” all over India. 

Footnote: In my library I have a book series called Charitravali, which are biographies dedicated to great people of India. I have written about these books in this blog. The Charitravali series also has the biography of C.V Raman, “The Scientist Extraordinary by Dilip.M.Salwi” ,which I used as a reference for this post. The entire series is a great read. I strongly recommend it to all my readers.  

Update:  Here is Priya’s explaination for the varying color of sea

The deeper the sea, the bluer it will be. Shallow water appears a lighter shade of blue or green. Yellow, Red, Green etc are absorbed first. The amount of organic debris in the water impacts the color. The deader it is (little or no organic debris or life-forms) the bluer it is.