A brief explanation of
"Raman Effect"

Sir Chandrashekhara Venkata Raman (7 November 1888 – 21 November 1970) was an Indian Tamil physicist born in the former Madras Province in India presently the state of Tamil Nadu. For the discovery of the "Raman effect" he was awarded 1930's Nobel Prize for Physics. Lets look into "Raman Effect" and why the discovery is important for science.

In physics worlds "Raman scattering" or the "Raman effect" is the inelastic scattering of a photon by molecules which are excited to higher energy levels.

Lets see this definition of each words in detail

Photon

In physics, a photon is a bundle of electromagnetic energy. It is the basic unit that makes up all light. The photon is sometimes referred to as a "quantum" of electromagnetic energy. Photons are not thought to be made up of smaller particles. They are a basic unit of nature called an elementary particle.

Light is particle or wave

Wave–particle duality is the concept in quantum mechanics that every particle or quantum entity may be partly described in terms not only of particles, but also of waves. Albert Einstein believed light is a particle (photon) and the flow of photons is a wave.

Scattering

Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more paths due to localized non-uniformities in the medium through which they pass.

When photons are scattered by a material, most of them are elastically scattered (Rayleigh scattering), such that the scattered photons have the same energy (frequency and wavelength) as the incident photons but different direction.

Inelastic scattering

However, a small fraction of the scattered photons (approximately 1 in 10 million) are scattered inelastically, with the scattered photons having an energy different from, and usually lower than, those of the incident photons.

In this scattering process, the incident photon interacts with matter (gas, liquid, and solid) and the frequency of the photon is shifted to red or blue. These are Raman scattered photons.

So what ?

Now we know that there are two type of scattering
1. Incident and scattered photons have the same energy (Rayleigh scattering)
2. Incident and scattered photons have the less or greater energy (Raman scattering)

Stokes and anti-Stokes

When atom or molecule absorbs energy scattered photon has less energy than the incident photon (Stokes Raman scattering) and when atom or molecule loses energy: scattered photon has more energy than the incident photon (anti-Stokes Raman scattering).

Raman spectrum

The spectrum of the scattered photons is termed the Raman spectrum.

Raman spectroscopy

So by analyzing the spectrum we can get a clue of the nature of the material the light is scattered from. Raman spectroscopy is commonly used to provide a structural fingerprint by which molecules can be identified.

Raman spectroscopy is used to analyze a wide range of materials, including gases, liquids, and solids. Highly complex materials such as biological organisms and human tissue can also be analyzed by Raman spectroscopy.