
Raman Spectroscopy
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:
- Only uses the 1064 nm laser - poor for sensitivity,poor for aqueous solutions, poor for highly colored samples.
- 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:
- 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
- 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.