C.V. Raman (1888. 11. 7 – 1970. 11. 21): An Indian physicist. He carried out ground-breaking work in the field of light scattering, which earned him the 1930 Nobel Prize for Physics. He discovered that when light interacts with a material, some of the scattered light changes wavelength. This phenomenon, subsequently known as Raman scattering, results from the Raman effect.
Principle of Raman spectroscopy
Raman scattering is a phenomenon in which a photon scatteres inelastically from the vibrational, rotational, or other low-lying states of the interacting material. This results in the change of the original frequency of the photon. Raman scattered light is mixed with photons of frequencies different from the original light. The difference between the initial frequency of the light source and the later frequency after interaction with the material is represented by the Raman spectrum. Since the Raman spectrum is unique for each material, it is used to identify unknown materials. In addition, physical and chemical changes in substances can be observed through analysis of Raman spectra.
A laser is used as the single frequency light source. The combination of various optical elements and a microscope, spectrograph, and photodetector forms a micro-Raman spectroscopy system that can measure very tiny samples.
Principle of Raman scattering
Schematic diagram of Raman system
Advantages of Raman spectroscopy
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Non-destructive measurement
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Identifying unknown materials
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Samples in gas, liquid, and solid states can be measured.
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Pretreatment of samples is not required in most cases
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Samples of very tiny size are measurable (spatial resolution of ~ μm with micro-Raman system)
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Hardly affected by moisture.
Raman Experiment Techniques
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Spontaneous Raman spectroscopy
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Resonant Raman spectroscopy
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Polarization dependent Raman spectroscopy
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Surface enhanced Raman spectroscopy
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Imaging byRaman mapping
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Temperature dependent Raman spectroscopy