What is a confocal Raman microscope?

A Raman microscope combines a Raman spectrometer with a standard optical microscope.  The excitation laser beam is focused through the microscope to create a micro-spot with a diameter in the order of 0.5-10 µm.  The Raman signal from the sample is collected from a similar area, passes back through the microscope into the spectrometer and is there analysed for spectral information.

The Raman microscope allows Raman spectroscopy to be performed with microscopic spatial resolution.  Thus it opens up a new dimension in chemical analysis:

  • Analysis and identification of individual particles with dimensions down to 0.5 µm.
  • Characterisation of sample features with dimensions down to 0.5 µm.
  • Location and identification of microscopic contaminants.
  • Raman mapping (imaging) of sample features to show distribution of components, with a spatial resolution down to 0.5 µm.

Simply adding a microscope assists in giving lateral (XY) spatial resolution, but does not give depth (Z) spatial resolution.  For this confocal optics are required.  There are several methods in use today, some truly confocal, others pseudo confocal, which work with varying success.  For a true confocal design (which incorporates a fully adjustable confocal pinhole aperture) micron depth resolution is possible, allowing individual layers of a sample to be discretely analysed.

The XploRA™ Raman microscope showing the optical microscope at the bottom, and the Raman spectrometer on top.
The XploRA™ Raman microscope showing the optical microscope at the bottom, and the Raman spectrometer on top.
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