Sampling laser rejection

Figure 8.4. Raman spectrum of liquid benzene from a single spectrograph with and without a holographic laser rejection filter between the sample and the entrance slit. Intensity scales differ greatly between the two spectra.

Figure 9.13. FT-Raman spectra of a mildly fluorescent, impure sample of ortho dinitrobenzene before (A) and after (B) correction for instrumental response. Modulation at A is caused by the laser rejection filter. (Adapted from Reference 4, p. 104.)...

The above describes the commonly utilized instrumentation required for dispersive Raman spectroscopic microscopy. In the past, Fourier transform Raman spectroscopy provided an alternative for coloured and fluorescent samples but the use of near-IR lasers at 1.064 pm together with In Ga As detectors reduced the sensitivity. Recent developments in laser rejection Alters and CCD technologies have rendered dispersive techniques the preferred option. 

Fig. 4.57. Example of sensitive Raman equipment. The band pass filter, BP, cleans the laser radiation. The high NA objective lens LI focuses the laser on the sample and collects the Raman scattered radiation within a large solid angle. The band-rejection filter, BR, blocks elasti-...

Flistorically, the second most important function of the Raman spectrometer was to reject scattered laser radiation. Because the laser scatter from the sample can be many millions of times more intense than the signal and cannot be rejected spatially, the power of the spectrometer to efficiently and... 

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