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Raman Spectroscopy Lab

The Department of Earth Sciences at the University of Gothenburg has a LabRAM HR Evolution Raman microscope equipped with a 532nm and a 785nm laser.

The instrument is ideally suited for both micro and macro measurements, and offers advanced confocal imaging capabilities in 2D and 3D. The LabRAM HR Evolution is a true confocal Raman microscope that enables most detailed images and analyses to be obtained with speed and confidence.

About Raman spectroscopy

Raman spectroscopy is a vibrational spectroscopic technique that is used to provide information on molecular and crystal structures, i.e. the method is capable of characterising organic and inorganic substances as well as various substance specific properties, such as crystallinity, orientation, residual stresses and to a certain degree also the chemical composition.

The Raman technique uses a laser light source to irradiate a sample, and generates a so-called Raman scattered light, which is detected as a Raman spectrum using a CCD camera. The characteristic fingerprinting Raman light spectra can be compared with an extensive database, which enables effective and fast identification of the basic properties of the investigated sample.

Following a general improvement in photon detection and computational capacity Raman spectroscopy has developed into a versatile and most important molecule characterization method that is used in material science, medicine, pharmaceutical production and research as well as in geosciences and forensics. Its predominant advantages are:

  • Raman spectroscopy is a non-contact and non-destructive analysis
  • It can investigate samples with high spatial resolution up to sub-micron scale
  • It allows in-depth analysis of transparent samples using a confocal optical system
  • There is no sample preparation needed.
  • Both organic and inorganic substances can be measured
  • Samples in various states such as gas, liquid, solution, solid, crystal, emulsion can be measured
  • Samples in a chamber can be measured through a glass window
  • Typically, only 10 msec to 1 sec exposure is needed to get a Raman spectrum
  • Imaging analysis is possible by scanning the motorized stage or laser beam

Raman scattering (Raman effect)

When light is scattered by matter, almost all of the scattering is an elastic process, so-called Rayleigh scattering. During Rayleigh scattering there is no change in energy and wavelength with regard to the incoming light. A very small percentage of scattering, however, is an inelastic process, thus the scattered light has different energy and wavelength from the incident light. This inelastic scattering of light is molecule and molecule property specific which can be used to characterize materials and their properties. The inelastic scattering of light was predicted theoretically by Adolf Smekal in 1923 and first observed experimentally by Chandrasekhara Venkata Raman in 1928, which is why this inelastic scattering is called Raman scattering (or the Raman effect).

Image source: www.nanophoton.net

During the interaction between light and matter the incident light excites electrons in the material which are transferred into an unstable energy state. The excited electrons fall back immediately to their ground state and the resulting energy is emitted as a scattered photon, which has the same energy as the incident photons. This process is called Rayleigh scattering. A very small portion of the excited electrons, however, do not fall back to the ground level, but stay at a slightly higher energy vibrational state. The scattered light has consequently a slightly different energy and wavelength, which is the so-called Raman scattered light. The energy difference between the incident light and the Raman scattered light is characteristic for molecules and their physico-chemical properties.

Image source: https://commons.wikimedia.org

There are two types of Raman scattering: (1) Stokes Raman scattering and (2) anti-Stokes Raman scattering. Stokes Raman scattered light has less energy (longer wavelength) than incident light as described in the paragraph above. By contrast, anti-Stokes Raman scattering is a process in which an electron is excited from the vibrational level to the ground level. It involves an energy transfer to the scattered photon thus anti-Stokes Raman scattered light has more energy (shorter wavelength) than incident light.

What is Raman spectroscopy used for?

Raman spectroscopy is used in a variety of fields. New applications arise almost every year. In general Raman spectroscopy is commonly used for:

  1. Identifying an unknown substance
  2. Identifying polymorphs
  3. Tracking changes in molecular structures
  4. Tracking a change in crystallinity
  5. Evaluating the magnitude of residual stress
  6. Assessing the direction of orientation of molecules


Matthias Konrad-Schmolke

Institutionen för geovetenskaper
Göteborgs univseritet

E-post: mks@gvc.gu.se
Telefon: 031 - 786 2864

Sidansvarig: Henrik Thelin|Sidan uppdaterades: 2018-10-18

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