Sir Chandrasekhara Venkata Raman

Sir Chandrasekhara Venkata Raman was a physicist from India well known for his role in light scattering. He and his student K. S. Krishnan spotted that light changes its wavelength and frequency when it passes through a transparent medium. Raman gained the Nobel Award in Physics in 1930 for his discovery, making him the first Asian to do so in any field of science. Sir Chandrasekhara Venkata Raman with the quartz spectrograph used to determine the wavelengths of the scattered light, resulting in the Raman Effect. The Government of India presented the first Bharat Ratna, the country’s highest national honour, to him in 1954. 

About Sir Chandrasekhara Venkata Raman

Raman was a native to Tamil Brahmin parents and completed his secondary and upper secondary schooling at St Aloysius’ Anglo-Indian High School at 11 and 13, respectively. At 16, he topped the University of Madras bachelor’s degree exams with honours in physics from Presidency College. While still a graduate student, he broadcast his first research work on light diffraction in 1906. 

 At 19, he reached the Indian Finance Service as an Assistant Accountant General in Calcutta. There he met India’s first research college,  the Indian Association for the Cultivation of Science which approved him to do an anonymous study and where he made significant discoveries in acoustics and optics.

Seeing the Mediterranean Sea on his first journey to Europe inspired him to reject the prevalent explanation for the sea’s blue colour at the time, reflecting Rayleigh-scattered light from the sky. In 1926, he entrenched the Indian Chronicle of Physics. In 1933, he relocated to Bangalore to become the first Indian administrator of the Indian Institute of Science. He started the Raman Research Institute in 1948, where he served until his death.

In 1922, he advertised his work on “Molecular Diffraction of Light,” which led to his ultimate detection of the radiation effect on February 28, 1928, and earned him the Nobel Award in Physics in 1930. His additional interests include colloidal optics, magnetic and electrical anisotropy, and the physiology of human vision. He is most recognised for establishing the ‘Raman Effect,’ or the idea of light scattering.  

In refraction, wave speed, frequency, and wavelength are critical. The wave slows, but its frequency stays constant since its wavelength is shorter. The frequency of waves remains constant while moving from one medium to another. Waves slow down, and their wavelength decreases as they move through the denser material.

On February 28, 1928, Raman and Krishnan used Raman’s own invention – the spectrograph – to get the first spectra for this novel scattering distinct from incoming light. A spectrograph is a device that separates incoming light by wavelength or frequency and records the resultant spectrum in a multichannel detector, such as a photographic plate. Many astronomical observations make use of telescopes as spectrographs.

Raman Spectroscopy

Raman spectroscopy is a type of spectroscopy commonly used to identify the vibrational modes of molecules while spinning and other low-frequency modes of systems can also be seen. Raman spectroscopy is extensively used in chemistry to generate a structural fingerprint that may be used to identify compounds.

Raman spectroscopy is predicated on inelastic photon scattering, also called Raman scattering. A homogenous light source is employed, often a laser in the visible, near-ultraviolet or near-infrared ranges; however, X-rays can also be used.

Because spontaneous Raman scattering is often relatively weak. For many years, the primary issue in obtaining Raman spectra was distinguishing the soft, inelastically scattered light from the powerful Rayleigh scattered laser light (“laser rejection”). The most common kind of spectrograph is a dispersive single-stage spectrograph (axial transmissive (AT) or Czerny–Turner (CT) monochromator combined with a CCD detector, however, Fourier transform (FT) spectrometers are also used with NIR lasers.

Raman Effect

When molecules deflect a light beam, the light changes its wavelength and frequency; when a light beam travels through a dust-free, transparent specimen of a chemical compound, a small percentage of the light penetrates directions dissimilar from the incident beam. The majority of dispersed light has the same wavelength. However, a minor portion has wavelengths that differ from the incoming light; its presence is due to the Raman effect. The effect was named after Indian physicist Sir Chandrasekhara Venkata Raman, who initially observed it in 1928.

The Raman effect is weak; for a liquid compound, the intensity of the impacted light may be as low as 1/100,000 of the power of the incident beam. The Raman line pattern is unique to each molecular species, and its strength is proportional to the number of scattering molecules along the light’s path. 

The energy associated with transitions between distinct rotational and vibrational states of the scattering molecule corresponds to Raman frequency shifts. Except for simple gaseous molecules, pure rotational changes are modest and difficult to detect. Rotational movements are hampered in liquids, and distinct rotational Raman lines are not seen.

Conclusion

In 1928, Sir Chandrasekhara Venkata Raman detected that when a transparent substance is irradiated by a beam of light of one frequency, a little fraction of the light exits at right angles to the initial direction. Some of this light is of other frequencies than the incident light. The energy associated with transitions between different rotational and vibrational states in the scattering material is called Raman frequencies. Raman also conducted experimental and theoretical research on the diffraction of light by ultrasonic and hypersonic acoustic waves and studied the impact of X-rays on infrared vibrations in crystals exposed to conventional light.