In practice - What is the difference between dispersive Raman and FT-Raman?

In practical terms FT-Raman is good in simple routine analysis but has many limitations, and thus it is generally used these days in routine measurements only:

  1. Only uses the 1064 nm laser - poor for sensitivity,poor for aqueous solutions, poor for highly colored samples.
  2. The optical construction limits the spatial resolution that can be achieved (this is why most FT manufacturers have abandoned FT-Raman microscopes).

The advantage of a dispersive Raman system is that it will offer both routine and research capabilities upon the one instrument including:

  1. Multiple laser wavelengths - this will enable sample and scattering properties to be optimized for a widest range of samples, enhancing sensitivity, penetration depth control, and fluorescence rejection - examples:

    • Green lasers can be good for inorganics and resonance Raman (eg. CNT and carbon) and SERS
    • Red or NIR lasers (eg. 780-830 nm)are good for supression of fluorescence, often at least as good as the FT-Raman 1064 nm laser
    • Red or Green lasers for aqueous solutions
    • UV lasers for resonance Raman on bio-molecules eg. Proteins

  2. The Raman microscope - a true confocal Raman microscope (FT-Raman optics do not enable this design to be used) will provide a spatial resolution of around 1 um. The use of a true confocal aperture has been well established in its ability to provide sensitive Raman images of samples- showing chemical composition, distribution, morphology and many other characteristics of a sample. See the Raman tutorial for further information.