Research Profile

by Roberto Lalli

Chandrasekhara Venkata Raman

Nobel Prize in Physics 1930
"for his work on the scattering of light and for the discovery of the effect named after him".

The Indian physicist Chandrasekhara Venkata Raman made original contributions to various fields of experimental physics, and is especially known for his achievements in the branches of acoustics and optics. His work on light scattering, which led to the discovery of the effect that bears his name in 1928, gained him the 1930 Nobel Prize in Physics. He was the first Asian scientist to win a Nobel Prize in science. Raman’s scientific activities had a deep impact on the evolution of scientific research in India. Not only was he an excellent teacher and intuitive researcher, able to attract and guide many Indian physicists of a younger generation. He also took the responsibility to organize scientific research in India by assuming various institutional roles and by establishing new institutional frameworks, including the Indian Academy of Science founded in 1934 and his private research institute—the Raman Research Institute—in Bangalore established in 1948. Raman’s achievements and their international recognition through several prizes and honours were instrumental in launching the Indian research tradition in modern science, with later important contributions to the production of scientific knowledge all through the 20th century.

Talented Part-Time Researcher
Chandrasekhara Venkataraman (latter split by him into Venkata Raman) was born on November 7, 1888, in a small village near Trichinopoly (now, Thiruchirapalli, Tamil Nanu) in southern India. He came from a cultured family of landholders. His father Chandrasekhara Iyer loved science and had become lecturer in physics and mathematics at the Hindu College in Vizagapatam. The young Raman inherited from his father a passion for science and music, and became a sort of child prodigy during his student years. In his teens, Raman received various scholarships and awards, earning his BA degree in 1904, when he was only sixteen years old. During his master’s degree studies in physics at the Presidency College, Madras, Raman did original experimental investigations in the field of optics. He also published his first article in an international journal at the age of eighteen. His first published work concerned the observation of the diffraction bands that appeared when the angle between the incident light and a prism’s face is very large. It was an extraordinary achievement, given that at the time there was no tradition of pursuing original research in India. The Presidency College was a teaching institution and was not equipped to do original research. In this condition, Raman developed a working style that would play a relevant role in his future endeavours. He was able to use his physical intuition and his observational skill to make better use of the materials he had at his disposal, without waiting for suitable and more expansive instruments. By the completion of his MA degree, he had showed that he would have been a talented scientist. Scientific careers, however, were precluded to those scholars who had not studied abroad for a certain period. (He could have studied in England after his BA, but he was prevented to do so by a negative medical assessment of his health conditions). Then, he decided to become a Civil Servant at the Finance Department in Calcutta in 1907, but he did not abandon scientific research.

In Calcutta, he began making research at the Indian Association for the Cultivation of Science, on early mornings, evenings and during holidays. Founded in 1876, this private institution was the oldest Indian institute devoted to basic research in various fields. When Raman decided to make the Indian Association for the Cultivation of Science his home institution, the Association was nearly inactive and was maintained by its secretary Amritlal Sarkar, who was the son of the doctor and social reformer Mahendralal Sarkar, founder of the Association. During his part-time work at the Association, between 1907 and 1917, Raman published about thirty articles containing original investigations in different branches of physics.
His achievements began to be noticed by both the international scientific community and the Indian academics. In 1917, philanthropic donations allowed the establishment of a chair for physics at the Calcutta University and it was decided to offer the position to Raman, breaking the rule that the professorship could be given only to scholars who had been trained abroad. Although the professional change was economically disadvantageous, Raman accepted the position and became Palit Professor of Physics, a position that he held till 1932. From 1917 onward, he could dedicate full-time efforts to physics working at both the University of Calcutta and the Association, of which he became the Honorary Secretary in 1919. It was an immensely productive period, during which he made the discovery that would shortly gain him the Nobel Prize in Physics: the discovery of the Raman Scattering.

Research in Acoustics and Optics
After he became Honorary Secretary of the Indian Association for the Cultivation of Science, Raman was able to improve the organizational structure of the institution in order to favour his own research interests. In this period he began attracting younger physicists both at the University and the Association, with whom he collaborated to pursue scientific research. His love for music led him to dedicate many of his first research projects to the field of acoustics. He produced important studies on vibrations and sounds and was interested in the theory of musical instruments. In this field, he studied the violin family and Indian drums, such as the mridangam and the table. In the 1920s he was recognized as one a world authority in the physics of musical instruments, as is showed by the request to write the issue of the Handbuch der Physik dedicated to such a topic in 1927.
Optics was the second field to which he dedicated major efforts, and in optics he achieved what is known as his major discovery. The discovery of the Raman effect was prepared by various years of strenuous observations of the optical properties of molecules in gases and liquids as well as those of emulsions and colloidal solutions. In this research, he developed a set of experimental methods that allowed him to become a renowned expert of optics and gave him a certain advantage in discovering the scattering effect that bears his name.

The Discovery of the Raman Effect
Since the late 19th century, it was understood that a tiny fraction of a light pencil passing though transparent medium is scattered in all directions. This effect was called Rayleigh scattering after Lord Rayleigh, the British physicist who developed the theory of light scattering from 1871 to 1889. The Rayleigh theory of scattering maintains that the scattering is elastic; namely, that the scattered light has the same wavelength of the incident light. In October 1923, working in the context of the Bohr-Sommerfeld theory of atomic structure and making use of the light-quantum hypothesis, the Austrian theoretical physicist Adolf Smekal predicted that a small part of the scattered light should be inelastic; namely, scattered radiation should also have frequencies different from that of the incident light because of the interaction between light quanta and the transitions between electronic states in atoms and molecules. Smekal’s prediction of incoherent scattering had a role in the extension of the quantum theory of dispersion Kramers began formulating in 1924. In mid-December 1924, Kramers, with the help of Heisenberg, completed the influential paper on the quantum theory of dispersion, which is considered one of the fundamental steps leading to the discovery of quantum mechanics or, more precisely, to the matrix formulation of quantum mechanics elaborated by Heisenberg, Born and Jordan in 1925.
In their paper on dispersion theory, Kramers and Heisenberg also analysed various types of incoherent scattering that included the ones predicted by Smekal. These results were later absorbed and clarified in the context of quantum mechanics. The existence of inelastic scattering, hence, became one of the predictions of quantum mechanics since its early formulation, but an empirical confirmation still lacked.
Raman began working on the scattering of light much before theoretical advances would make the observation of the inelastic scattering a confirmation of a novel theoretical scheme. His interest was sparked by the strong impression made on him by the deep blue of the Mediterranean Sea during his first travel abroad in 1921. The impression was so strong that he began investigating the reason for the emergence of the blue colour of the sea during his return trip. Lord Rayleigh had explained the colour of skylight in his theoretical work on light scattering. The colour of the skylight depended on the scattering of sunlight by the molecules of air, because short-wavelength radiation is scattered more than radiation of higher wavelength. Rayleigh, however, had not extended this explanation to include the colour of the sea. For him, this was only an effect of the reflection of the colour of skylight. Raman was unconvinced by this explanation, and by means of ingenious methods he disproved Rayleigh’s reasoning and proved that the blueness of the sea was due to the scattering of sunlight by water molecules.

In Calcutta, he continued working intensively on the scattering of light, establishing a program devoted to the investigation of several features of this phenomenon when light passed through different transparent media. He ingeniously developed methods that allowed the exploration of subtle aspects of the scattering phenomenon. In the mid-1920s, he was internationally renowned as an expert in the fields of acoustics and optics, as is showed by the fact that he was elected Fellow of the Royal Society in 1924.
In the elaboration of his method to investigate light scattering he discovered the difficult-to-observe Raman effect by February 1928. Working with his younger collaborator Kariamanickam Srinivasa Krishnan at the Indian Association for the Cultivation of Science, he was able to refine the observation to such a degree that scattered light of frequency different from that of the incident light was detected. Moreover, the numerous observations made by Raman and Krishnan, with different purified liquids (and the re-interpretation of previous observation made by other collaborators at the Association) allowed them to rule out the alternative explanation that this effect was due to fluorescence due to impurities in the scattering material. At the end of February, Raman and Krishnan made a refined experiment using as source a mercury arc instead of filtered sunlight. Using a small spectroscope, they observed that scattered light contained two lines at wavelengths that were not in the incident beam. They considered this moment the discovery of what is now called the Raman effect, although it was more of a culmination of a seven-year research program. Their papers announcing the discovery were published in Nature in March, April, and May 1928. The discovery of the Raman effect was soon considered of great importance, also because it was in agreement with the prediction of the recently developed quantum mechanics. Moreover, the Raman scattering had the potentiality to become a fundamental tool in physics and chemistry for it allowed the spectroscopic study of the structure of molecules and in this sense it became a field of research of its own (and even more so in the 1960s after the invention of the laser). In a few months, many other scientists confirmed the existence of effect. The Soviet physicists Grigory Samuilovich Landsberg and Leonid Isaakovich Mandelstam had also discovered the effect in crystals independently on, and simultaneously to, Raman, but publicly announced the achievement only after Raman and Krishnan had published their papers in Nature. For this reason, Raman was perceived as the discoverer of the new scattering with changing frequency by the great majority of physicists and the effect was given his name. Since 1928 the effect was called the Raman effect everywhere but in the Soviet Union, where scientists continued calling it the “combination scattering” until the 1970s. Raman received two nominations a few months after the discovery and, after the number of nominations had reached ten, he was awarded the eminent prize in 1930 “for his work on the scattering of light and for the discovery of the effect named after him.”
Raman was indeed conscious of the strong competition and he rushed to obtain priority for the discovery by working intensively and by assuring speedy publication of the results. This strategy gained him a full Nobel Prize, which made him the first Asian scientist to receive this prize in science. This achievement is even more relevant if one thinks of the setup with which Raman made the initial discovery. It consisted of very simple and inexpensive instrumentation: benzene, a mercury lamp, a suitable filter, a small spectroscope, and a glass condensing lens. The Nobel Prize to Raman had a strong importance for the evolution of scientific research, especially physics research, in India. Raman soon had the opportunity to employ the international recognition to obtain more funds to promote scientific research in India. Moreover, the discovery itself showed that important scientific results could be achieved without expensive instrumentation and, hence, increased the self-confidence of Indian scientists and of a younger generation of students.

Research on Diamonds and the Construction of New Institutional Bodies
After the discovery of the Raman effect, Raman developed a long-lasting interest in the optical properties of diamonds and studied the scattering of light in various types of diamonds. Diamonds, for him, could be the material that, if thoroughly investigated, could allow a complete understanding of the properties of crystalline structure. His investigations included research on fluorescence, luminescence, photo-conductivity, ultra-violet transparency, birefringence, absorption, X-rays, specific heat, the Faraday effect, magnetic susceptibility, etc. In the pursuit of this research, which lasted till the end of Raman’s scientific life, he built one of the largest collections of diamonds with about five hundred of them.
In 1933, Raman was called to become the director of the Indian Institute of Science in Bangalore, but he resigned after only four years because of increasing tensions between him and the governing board. He remained Professor of Physics there till 1948, when he became the first National Professor in the Government of India, which had become independent the year before. In 1934, he had also founded the Indian Academy of Sciences (IAS) in Bangalore, which grouped authoritative scientists coming from different parts of India to promote scientific research in their country. Raman was very involved in the activities of the Academy as its President from its establishment till his death in 1970. Using his role of President of the IAS he was also able to found his own private research institute in a piece of land donated in 1934 by the Government of Mysore to the Academy. Raman collected private donations sufficient to start the construction of a small edifice in the early 1940s. The institute was inaugurated as the Raman Research Institute in 1948, when he was able to work exclusively as the director at this institution after his resignation from the Indian Institute of Science.
When Raman was alive, the Institute and the Academy were related by the fact that Raman was the greatest authority in both the institutions. As the first Indian Nobel Laureate in science he enjoyed an enormous prestige, which allowed him to raise enough private donations to make the Raman Research Institute independent of public funding. At the Institute, Raman worked with many collaborators on a large variety of topics, but with a special focus on optics. In that field, Raman and his co-workers investigated the properties of diamonds, the colours of flowers, and the physiology of vision. When Raman died at the age of eighty-two, the scientific and political situation in his home country had changed dramatically. Raman stands out as one of the major protagonists in this scientific transformation and in the establishment of a strong scientific tradition in India, also in virtue of the prestige given him by the Nobel Prize.

Bibliography

Bhagavantam, S. (1971) Chandrasekhara Venkata Raman 1888-1970. Biographical Memoirs of Fellows of the Royal Society 17: 564–526.

Mehra, R. & Reichenberg H. (1982) The Historical Development of Quantum Theory. Vol. 2. The discovery of Quantum Mechanics. Springer, Dordrecht.

Miller, F. A, & Kauffman, G. (1989) C. V. Raman and the Discovery of the Raman effect. Journal of Chemical Education 66: 795–801.

Raman C. V. (1930) Nobel Lecture: The Molecular Scattering of Light. Nobelprize.org. Nobel Media AB 2014. Retrieved 18 July 2015. http://www.nobelprize.org/nobel_prizes/physics/laureates/1930/raman-lecture.html



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