Indian physicist Chandrasekhara Venkata Raman discovered how the scattering of light by gas, liquid, or solid molecules causes a change in the wavelength of light—the effect known as Raman scattering. The spectrum called Raman spectrum, which is emerged from this scattering is used in the identification and analysis of the structure of molecules. With this discovery, Raman received the title of knight and was the first Asian to win a Nobel Prize in 1930.
Who is Chandrasekhara Venkata Raman?
C.V. Raman was born in the village of Thiruvanaikaval near Tiruchirappalli in the Tamil Nadu, southern Indian province. Her father, Chandrasekhara Iyer, was a professor of physics and mathematics. Raman went to Presidency College in Madras for graduate education. He wrote his first research published here, his article on optics "Unsymmetrical Diffraction" appeared in the British Philosophical Magazine. In colonial times it was not possible to pursue a scientific research career in India without graduating from British universities.
Thus, Raman took the highly demanded Indian Government Financial Audit and Accounting exams and came first in them. In 1907, he was appointed as an assistant general accountant and worked as an accountant in Calcutta for 10 years. Shortly after he arrived in Calcutta, he came across the Indian Association for the Cultivation of Science, which was established for Mahendralal Sircar. Despite the limited possibilities of society, Raman started to work here in his spare time. In his first prominent work, he expanded the definition of the fundamental vibration modes—previously proposed by Hermann von Helmholtz—into more complex modes.
C. V. Raman's work in the community caught the attention of Sir Ashutosh Mukherjee, the founder of the University of Calcutta, who offered him the post of Palit professor of physics. Raman accepted this proposal in 1917, which would mean leaving the lucrative civil service and face serious losses in salary.
Raman made his first trip abroad to England in 1921 by participating in a scientific conference attended by representatives from universities in the British Empire. While returning to India by sea, the intense blue color of the Mediterranean attracted his attention. Physicist Lord Rayleigh explained this event as the reflection of the blue color in the sky over the sea as a result of the elastic scattering of the sunlight (Rayleigh scattering) in the atmosphere. However, observing the sea surface with a light-polarizing device called the Nicol prism in a 53-degree angle (Brewster angle) proved that this explanation was insufficient.
After the experiments conducted in Calcutta, C. V. Raman concluded that the blue color of the water comes from the light emitted by the water molecules, just as the blue color of the sky originating from the scattering of the sunlight emitted by the air molecules. In 1922, this discovery appeared in Raman's small book named Molecular Diffraction of Light, ultimately leading to intense experimentation and the discovery of the famous effect bearing his name.
Shedding light on scattered light
C.V. Raman scattering was first noticed in Raman's lab around 1923 and was published in the periodical Indian Journal of Physics, which Raman founded in 1928. In addition to the primary Rayleigh scattering components that have the same frequency as the incident light, Raman also saw that there is a weaker secondary component with a variable frequency (i.e. energy level).
Initially, Raman scattering was thought to be due to fluorescence, but Raman eliminated this possibility by showing that the scattered light was highly polarized, with the experiments conducted with K.S. Krishnan. Raman realized that the second beam he observed in early 1928 was the optical analogue of the X-ray—the Compton scattering discovered by Arthur Compton in 1923, scattering X-rays passing through the substance and forming a longer wavelength.
Under the Compton effect, X-ray radiation behaves like quantized particles (photons) that enter into an elastic collision with the electrons in the substance. This effect was determining evidence of the presence of such quantities that are proportional to their frequency of energy and momentum. In Raman scattering, visible light acts as quantized particles that enter an inelastic collision with the molecules. Raman scattering has either a lower or higher frequency than the radiation that it interacts with, depending on whether the light quantum energizes the molecule or absorbs energy from it. The theory was envisioned by Werner Heisenberg and Hendrik Kramers in their studies on the quantum theory of scattering in 1925. The Raman scattering thus provided strong evidence of the quantized nature of light.
The main significance of the Raman effect was that it provided a powerful technique that allowed to study molecular structures and energy levels. In the Raman spectrum, the shift in frequency between interacting radiation and secondary radiation is directly related to the difference between initial and final molecular energy levels, and therefore Raman scattering can be used to detect certain molecules and chemical bonds. The first gathered information mostly includes the rotation and vibration levels of the molecules. These were previously available only from the infrared spectrum and were difficult to obtain. The Raman spectroscopy made this kind of information more affordable, and accessible.
Other achievements of Chandrasekhara Venkata Raman
With the discovery of the laser in the 1960s, Raman spectroscopy was further developed and finalized. This enabled the technique to be used in microscopic examinations and measurements of the substance. Today, it serves many different functions in many different fields, from real-time monitoring of anesthetic gas during surgical interventions in medicine to the protection of historical monuments, and including its use by law enforcement and security services in detecting drugs and explosives and forensic trace evidence.
In 1933, Chandrasekhara Venkata Raman left Calcutta to join the Indian Institute of Science in Bangalore as the first Indian executive. He trained a large number of students who served in important positions in both Calcutta and Bangalore. Although he left the management position four years later, he continued to teach as a physics professor until his retirement in 1948. After retirement, he founded the Raman Research Institute, where he worked on the optics of minerals and the physiology of vision. His most notable contribution of this period is the Raman-Nath theory of diffraction of light by ultrasonic waves.
In the 1940s, Raman studied Max Cage and Born-Van Karman's theory of lattice vibrations. This theory predicted partial continuity for the Raman spectrum, but Raman found significant distinct features in the spectrum of the diamond. The solution to this dispute was provided by other scientists in 1953: The discrete features observed were attributed to singularities that exist in some of the normal modes in partial continuity.
Chandrasekhara Venkata Raman was a true nature lover, whether the color of the sea or the minerals, the beauty of nature fascinated him. He was pleased by the sound, which led him to work on musical instruments and in domes with good acoustics where whispers are heard from everywhere. He celebrated the natural beauty with his science by researching physics.
Chandrasekhara Venkata Raman quotes
- "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."
- "You can't always choose who comes into your life but you can learn what lesson they teach you. Success can come to you by courageous devotion to the task lying in front of you."
- "I strongly believe that fundamental science cannot be driven by instructional, industrial and government or military pressures."
- "In the history of science, we often find that the study of some natural phenomenon has been the starting point in the development of a new branch of knowledge."