Two alternative methods of Raman imaging, via global (wide-field) illumination and via point illumination in combination with confocal light collection, have been applied to the study of heterogeneous polymer systems. From the results obtained it becomes apparent that the fluorescence inherent to most polymer systems severely limits the use of global illumination. Furthermore, the lack in depth resolution in Raman imaging by global illumination ruled out this method for the study of bulk polymer samples. Also as a consequence of the absence of depth resolution, the global illumination technique appeared more vulnerable to artifacts arising from scattering effects due to the sample geometry and fluorescence. Hence, for a general application of Raman imaging to the study of polymer samples, Raman imaging by point illumination in conjunction with confocal light collection is the method of choice

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An optical prefilter called Xtranotch, incorporating multiple holographic notch filters (or more generally Bragg diffraction notch filters) has been designed to record, with a single-stage spectrograph, both Stokes and anti-Stokes regions of the Raman spectrum simultaneously, with the smallest possible blind region around the Rayleigh line compatible with the best performance of current supernotch holographic filters. Thus, with this arrangement it is possible to observe simultaneously low-wavenumber Raman lines down to ca 28 cm −1 on each side of the Rayleigh line together with a high signal throughput along the entire spectrum. Optical alignment of this multi-notch filter is made easier owing to the use of a mechanical system which compensates for the beam deviation occurring when Bragg diffraction notch filters are rotated. Better laser line rejection can also be obtained by replacing one of the holographic notch filters by a more efficient grating filter but at the expense of throughput in the low-wavenumber region.