Raman - An Historical Perspective

          The work of Maxwell Planck highlighted the concept that light had properties of both waves and particles.  The energy of the light particle (photon) is quantized, each particle of light "carrying" with it a quanta of energy. Scientific discoveries immediately preceding the original publication of C.V. Raman's historical experiment demonstrated that electromagnetic radiation could be inelastically scattered as a result of interaction with molecules.  An inelastic scatter results when some of the energy of the electromagnetic radiation put into a molecule is absorbed, the remaining portion of the energy is emited. The resulting energy emission from the molecule is lower in energy than the original.  In 1928 C.V. Raman, in collaboration with K.S. Krishnan, published their light scattering experimental results in Nature.  It was in this article that Raman explained the basis for the Raman Spectroscopy theory: molecular transitions caused by incident light will inelastically scatter the light. (16) To read the text of Sir Raman's original article, click on this link.

Photo 7: C.V. Raman

Figure 14: A light of a different color
       In his original experiment, Raman focused a beam of sunlight and passed this beam through a green filter.  The green light was then passed through a solution of chloroform.  Raman was able to detect a faint yellow emission of light from the chloroform.  The green light (higher energy) was inelastically scattered by the chloroform and the resulting emission of yellow light (lower energy) was his proof.  As a result of this ground-breaking work, Raman received the Nobel Prize.
    Raman Spectroscopy and Spectrophotometers have come a long way since Sir Raman performed his original experiments. This analytical technique was facilitated by replacing the incident light source (sunlight) with LASER light.  Since the intensity of emitted light is a factor of 104 less than the incident light, using a LASER for input greatly enhanced the output signal of the scattered light. (16)

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