Single-Point Raman Microspectroscopy

In this chapter, some general principles and instrumentation for Raman microscopy are considered initially, in the context of a discussion of singlepoint microspectroscopy. After that, several varieties of imaging modes and data presentation are addressed. 

The spatial resolution is determined by either the laser spot size or the collection optics, both of which are ultimately limited by diffraction. The laser beam diameter at the focal spot (twice the beam waist, wq) was discussed in Chapter 6, and is given by Eq. (6.2)  

An alternative expression relates wq to the pupil (or aperture) of the objective lens, Wj.  

For single-point microscopy, the laser spot size often defines the spatial resolution, and the spectrometer is designed to collect light from an area 

Microscope Objective Working Distance (mm) Spot Diameter (2 Wo, pm, for 514.5 nm laser) Observed Depth of Focus (5a ) Power Density (W cm ) 

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Figure 11.7. Single-point Raman microspectroscopy of a pressed tablet containing acetami-dophenol and microcrystalline cellulose. The macro was obtained with an loo pm-diameter sampling area, and the micro spectra were obtained at the locations indicated.

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