THE INDIAN PRODIGY-DR. CV RAMAN

-       By Manvendu

-       Batch(2k18), Deptt. of Chemical Engg.

-       BIT Sindri, Dhanbad

INTRODUCTION

In the year 1930, Norwegian Nobel Committee announced Sir Chandrashekhara Venkata Raman, the 2^nd Asian and the first Non-white Individual as the Nobel Prize winner in the branch of Science, for his famous Experiment on Scattering of light, known after him as Raman Effect or Raman Scattering.

 Before discussing about the experiment, let’s know about the Experimenter.

      

         Dr. CV Raman

(Nov 7, 1888 - Nov 21, 1970)

 

LIFE OF A WONDERKIND

Born to Chandrasekhara Ramanathan Iyer and Parvathi Ammal, Raman was a prodigy. He topped Bachelor’s Degree Examination at University of Madras with Physics Honours from Presidency College at age of just 16!!!

His first research paper was published in 1906 on Diffraction of light, when he was pursuing Graduation. He joined the Indian Finance Service in Kolkata as Assistant Accountant General, when he was 19. Later, he got familiar with IACS(Indian Association for the Cultivation of Science),which happened to be the first Research Institute in India and it helped him to research independently. 

His major contributions are in the field of Optics and Acoustics (a Branch of Physics that deals with the study of mechanical waves in matters; such as vibration & sound). He was a gifted teacher as well. One of his students was Vikram Ambalal Sarabhai 

(a famous Physicist and Astronomer, who initiated Space Research & helped develop nuclear power in India & thus referred to as the Father of the Indian Space Program). 

In 1933, he moved to IISc(Indian Institute of Science) in Bangalore to become its first Indian Director. The same year he founded the Indian Academy of Sciences there. 

In 1948, he went on to establish Raman Research Institute, where he worked till his last days. Government of India honoured him with its Highest civilian award, Bharat Ratna in 1954 along with Rajaji C. Rajagopalachari and Dr. Sarvepalli Radhakrishnan. At the end of October 1970, Raman had a cardiac arrest and collapsed in his laboratory. Two days before Raman died, he told one of his former students, 

"Do not allow the journals of the Academy to die, for they are the sensitive indicators of the quality of science being done in the country & whether science is taking root in it or not". 

He died from natural causes early the next morning on 21 November 1970 at the age 

of 82. On the news of Raman's death, the then Prime Minister, Smt. Indira Gandhi publicly announced:

“The country, the House [of Parliament], and everyone of us will mourn the death of Dr. C. V. Raman. He was the greatest scientist of modern India and one of the greatest intellects our country has produced in its long history. His mind was like the diamond, which he studied and explained. His life's work consisted in throwing light upon the nature of lights, and the world honoured him in many ways for the new knowledge which he won for science.”

THEORY THAT CHANGED ASPECTS

Now, let’s explore about the Experiment which brought to him the most glorified award:

First of all, let’s understand what Raman’s scattering is?

It is the scattering of photons by matter inelastically, which generally involves vibrational energy being gained by a molecule with lowering in energy of visible laser.

When photons are scattered, most of them obey Rayleigh criteria (elastic scattering), which has an intensity of 0.1 to 0.01% of the source. Approximately 1 in 10 million photons can be scattered inelastically and the scattered photons having usually lower energy than the incident ones are called Raman scattered photons.

 FIG: An early Raman spectrum of benzene published by Raman and Krishnan

 

THEORY HISTORY

In January of 1928, Sir Kariamanikkam Srinivasa Krishnan, a student of Sir CV Raman started the Experiment. On 7^th of the month, he found that no matter what kind of pure liquid he used, it always produced polarised fluorescence within the Visible Spectrum of light. He and Raman named the new phenomenon as "modified scattering" with reference to the Compton effect as unmodified scattering. They sent a manuscript to a magazine named Nature titled "A new type of secondary radiation" on Feb 16^th, which was published on 31 March.

They obtained spectra of the modified scattering separate from the incident light on Feb 28^th of 1928. Due to the difficulty in measuring wavelengths of light, they had been relying on visual observation of the colour produced from sunlight through prism. Raman had invented an Instrument for detecting and measuring electromagnetic waves called Spectrographs. The Instrument made use of monochromatic light from a mercury arc lamp, which penetrated transparent material and was allowed to fall on a spectrograph to record its spectrum. The lines of scattering could now be measured and photographed.

 

PUBLIC DECLARATION

Raman made the announcement to the press. The Associated Press of India (now known as PTI) reported it the next day on Feb 29th, as "New theory of radiation: Prof. Raman's Discovery" as:

Prof. C. V. Raman, F.R.S., of the Calcutta University, has made a discovery which promises to be of fundamental significance to physics... The new phenomenon exhibit features even more startling than those discovered by Prof. Compton with X-rays. The principal feature observed is that when matter is excited by light of one colour, the atoms contained in it emit light of two colours, one of which is different from the exciting colour and is lower down the spectrum. The astonishing thing is that the altered colour is quite independent of the nature of the substance used.

To commemorate the discovery of Raman effect, Feb 28^th of every year is celebrated as the National Science Day in India.

APPLICATION ASPECTS

 

Ø               The effect is used by chemists and physicists to gain information about materials by examining rotational energy (for gas samples) and Electronic Energy Level (for X-ray source) through Raman Spectroscopy. It employs the Raman effect for substance analysis. The spectrum of the Raman-scattered light depends on the molecular constituents present and their state, allowing the spectrum to be used for material identification and analysis. Highly complex materials such as biological organisms and human tissue can also be analysed by Raman spectroscopy.

Ø               For solid materials, Raman scattering is used as a tool to detect high-frequency Phonon (vibration of atomic lattice) and Magnon (quasiparticle, a collective excitation of the electrons' spin structure in a crystal lattice) excitation.

Ø               Raman LIDAR (a method for measuring distances by illuminating the target with LASER light and measuring the reflection with a sensor) is used in Atmospheric Physics to measure the atmospheric extinction coefficient and the water vapour vertical distribution.

Ø               Stimulated Raman transitions are also widely used for manipulating a trapped ion's energy levels, and thus basis Qubit (basic unit of quantum information-the quantum version of the classical binary bit physically realized with a two-state device) states.

Ø               Raman spectroscopy can be used to determine the Force constant and bond length for molecules that do not have an infrared absorption spectrum.

Ø               Raman amplification is used in optical amplifiers.

Ø               The Raman effect is also involved in producing the appearance of the blue sky.

Ø               Raman spectroscopy has been used to chemically image small molecules, such as nucleic acids in biological systems by a vibrational tag.

 

FIG: Schematic of a dispersive Raman spectroscopy setup in a 180° backscattering arrangement

 

 

 

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