The Sea Is Blue, Raman Effect Discovers and Raman Effect On The World

The Biography of Famous Personalities of India will tell you about the controversies, the dark sides of a person that you may have never heard of.

The Sea Is Blue, Raman Effect Discovers and Raman Effect On The World

The Sea Is Blue The Raman Way

The University of Calcutta conferred on Raman an honorary doctorate in 1921. Soon after, he made his first visit to overseas. It was a formal visit to attend the University Congress at Oxford, where he represented Calcutta University. During his return journey to India, Raman spent hours watching the sea from the deck of his ship and was awestruck by its colour. According to Lord Rayleigh, who had explained the blue colour of the sea, ‘The dark blue of the deep sea has nothing to do with the colour of water but is simply the blue of the sky seen in reflection’. Fascinated by it, Raman watched the sea intently and using the simple optical tools he usually carries. He did experiments to capture the colour of the sea. When ship finally docked at Bombay, Raman’s paper explaining his observations on the Mediterranean Sea was on its way to the journal Nature.

During his return journey, Raman discovered that water molecules could scatter fight just like air molecules. It was very important and radical in those days. It paves way for Raman to discovering the famous Raman Effect. He wrote a brilliant essay in 1922, titled, “The Molecular Diffraction of Light”, in which he speculated that fight may exist in quanta, that is, massless particles of energy. This is an accepted theory till today but considered as the mos radical in those days. This research further proved to be important in his later life and it brought laurels to hi: country. Raman had a hunch that if the light did not exis as particles, or quanta, then scattering experiments woulc show only a change in the light intensity and not in its frequency, or colour.

On the other hand, if light did exisi in particles, or quanta, then a scattering of the light could change its frequency as well as intensity. He moved forward, giving a deaf ear to what others say, directed all research at the institute towards finding evidence for the corpuscular theory of light through scattering experiments. However, in 1923, with the discovery of the Compton effect, the existence of light quanta was established beyond doubt. With this success, Raman directed his team to work on light scattering. Initially their research findings were weak, some of his students named their initial finding as ‘feeble fluorescence’.

Raman’s team had to work rigorously four more years to be sure of what experiment they were doing. It was in 1927, they were able to say confidently that the new effect was not ‘a type of fluorescence’ but a modified scattering. This led to the discovery made on 28 February of the fact that light can undergo a scattering through a liquid resulting in a change in its frequency – the famous Raman Effect. To commemorate this historic event, this date is celebrated today as National Science Day.

Professor Raman’s work on the scattering of x-rays by liquids was also a pioneering one, and formed the basis of molecular structure studies in liquids. His paper along with collaborator Ramanathan has become extremely famous, and was a pioneering contribution made as early as in 1923. In the same year, Professor Raman advanced a theory of viscosity which has been used to explain the viscosity of polymers.
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In 1924, Professor Raman was elected as a Fellow of the Royal Society. At the meeting that was held to felicitate him, he expressed his appreciation for the honour he received. However, he went on to say that he did not consider this honour to be the ultimate and that he would, within 5 years, get the Nobel Prize for india. This confidence, determination, working toward specific goals, was characteristic of Raman’s personality. It can certainly be argued that after all it could have been a matter of the chance that he would not get the Nobel Prize, it may also be said that Raman had a fair idea of his research caliber.

In 1922, Professor Raman published a monograph entitled “The Molecular Diffraction of Light”. The seeds of his subsequent work can be found in this work. In this monograph, for example, he has considered in details how energy could be transferred between a quantum of light and a molecule of liquid. He had expressed his conviction in this celebrated monograph, that the quantum nature of light must manifest itself in molecular scattering.

Raman Discovers Raman Effect

In the month of April 1923, Professor Raman’s distinguished student, K.R.Ramanathan, initiated some experiments on the scattering of light by water. The experiment was done using sunlight, and the scattered light was seen as a track in the transverse direction, and using a system of filters, the scattered light was examined. The filters were arranged in such a way that when the incident light was passed through one of the two
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complementary filters and the scattered light was viewed through the other filter, no track should have been visible at all. Some track however could be observed, and was attributed to a weak fluorescence of the impurity molecules. Ramanathan himself wrote later that it was Professor Raman himself, and none other, who was not satisfied by the explanation based on the fluorescence model and that he (Raman) wondered if the track observed was due to some characteristic molecular scattering. The same effect was observed later in many organic liquids by K.S.Krishnan, another of Raman’s distinguished students.

There was a certain similarity in the explanation Raman had in mind with that of what is known as the Compton Effect. In the winter of 1927, Professor Raman went to Waltair for a short visit; he derived a formula for molecular scattering now known as the Compton-Raman formula.

In January 1928, another associate of Professor Raman, Venkateswaran, observed that in pure glycerin, the scattered light was greenish in color, instead of the usual blue. Moreover, the radiation was strongly polarized. In the last week of January, Professor Raman asked K.S. Krishnan to repeat these experiments under more carefully controlled conditions.

K.S. Krishnan was at that time doing completely theoretical work and Professor Raman advised him that it was not healthy for a man of science to stay out of touch with actual experiments for any significant length of time. Krishnan also reported the same type of findings as Ramanathan did, and Professor Raman personally verified all the observations.

Professor Raman was extremely excited about the findings, since he understood exactly what this just discovered phenomenon was. On 16th February, Raman sent a note to Nature, suggesting that the modified radiation observed in these scattering experiments could be due to certain molecular fluctuations. Yet, however, the phenomenon was not fully understood. On the 27th February, Raman set up an experiment in which he decided to view the track earlier thought to be due to fluorescence using a direct vision spectroscope. The experiment could not be completed that evening, as by the time the experiment was set up, the sun had set. Next morning, February 28th, 1928, when the experiment was done personally by Professor Raman, he found that the track contained not only the incident color but also another one separated by a dark region. This was the very first observation of what is known as the Raman Effect.

An announcement was made to the Associated Press on 29th February (in the leap year) and Professor Raman sent a note to Nature on March 8th announcing his discovery along with a complete explanation.

The Raman Effect, first announced in the Indian Journal of Physics in 1928, was named by the Royal Society of London as “among the best three or four discoveries in experimental physics of the decade.” The discovery not only opened up a new branch of spectroscopy, it has contributed enormously to our knowledge of the structure and dynamics of molecules and crystals. Recently, the Raman Effect has been exploited in the design of masers and lasers, to make available more frequencies than would otherwise be possible. The fact that nearly 10,000 papers have been published so far on Raman Effect and allied phenomena from all over the world speaks for itself of the importance of the discovery.

Raman : A World Class Scientist

Scientists of many countries appreciated the research papers of Raman and his colleagues. The Royal Society, the oldest and the most important science society of England, honoured Raman in 1924 by electing him as its ‘Fellow’ (that is, a member).

The annual session of ‘The British Association for the Cultivation of Science’ was held in the same year in Toronto (Canada). Raman inaugurated the seminar on the scattering of light. R.A. Millikan, the famous American Physicist, who also attended, was full of admiration for Raman. They became fast friends too.

At the Mount Wilson Observatory in California (U.S.A), a telescope of 100-inch width was in use. Those were the times when discoveries in the field of astronomy (study of stars and planets and their movements) filled people with wonder. Raman was always eager to learn new things. He spent a couple of days on Mount Wilson. During the nights he viewed the Nebula (bright or dark patch in the sky caused by distant stars or a cloud of gas or dust) through the telescope and was thrilled.

He went to Russia in 1925 to participate in the two hundredth anniversary of the ‘Russian Academy of Sciences’.

The Raman Effect On The World

Several laboratories in the world, on coming to know of this experiment, repeated such measurements and confirmed the findings. The recognition that followed in terms of the Nobel prize was almost inevitable, despite the fact that Raman was an Indian. The Nobel prize for Physics is given each year at Stockholm, Sweden, on the 10th of December, and the award is announced for that year about a month in advance. The Nobel committee meetings are held in great secrecy and between the time of announcement and the award ceremony, it would be very difficult to manage a journey to Sweden at such a short notice. Raman, however, made the trip, as even before the award was announced, he had already booked 2 tickets on a steamer, for himself and for his wife.

The Raman effect involves an exchange of a quantum of energy between a molecule and the electromagnetic radiation. Molecular energy levels are quantized, and this means that a molecule cannot possess an arbitrary amount of energy. The energy may be due to various reasons, and one may thus speak of the electronic energy, rotational energy or the vibrational energy of the molecule. A molecule may undergo transition from one energy state to another only by absorbing or emitting a discrete amount of energy. Raman Spectroscopy involves the study of such transitions. This is now an extremely specialized branch of spectroscopy and has undergone enormous developments. Raman spectroscopy is rarely done using sunlight as a source.

Now, Laser radiation is employed and it has very many fascinating applications, and the technique is known as the Laser-Raman Spectroscopy.