Raman Effect

"The velocity of light in a medium depends upon its index of refraction which in turn depends upon the wavelengths of the light, a process known as dispersion. In 1922 the English theoretical physicist Charles G. Darwin ( 1887- 1962) attempted to explain dispersion, unsuccessfully,on the basis of quantum theory. Raman and his associate K.S. Krishnan made their discovery while searching for an optical analogue of the Compton effect. Raman noted that in 1922 he and his student Rao had observed the depolarization of water as a function of wavelength, which changed for example,by 13.2,10.2, 11.5, 15.3 and 21.7 percent for red, yellow, green, blue and violet light."

Sir CV Raman, a world renowned Physicist, on February 28, 1928, made a path-breaking discovery which later was named as the Raman effect. This day is celebrated as National Science Day.

Barry Masters describes the life and legacy of one of the most important optical scientists of the 20th century.

a very clear explanation about Sir C V Raman's life history and about Raman effect.

When a photon hits an atom, it usually bounces back without losing any of it's energy. This is known as Rayleigh Scattering. Sometimes, a photon will leave some of it's energy with the atom. When it bounces back, it will have a different energy. This is known as Raman Scattering. Atoms can only accept very specific quantities of energy, the exact quantities they can accept determine what kind of atom it is. (This is related to the effect that causes elements to have different chemical properties, it also accounts for an element's emission spectrum). By ignoring Rayleigh Scattering, and by measuring the exact quantities of energy accepted by the atoms in question, it is possible to determine exactly what element caused the scattering. This is known as Raman Spectroscopy.