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From what I have gathered regarding the schematics of Raman spectrometers, the notch filter is used to remove a narrow range of light corresponding to that of the laser used to excite the sample. How is this accomplished? I can't find a reference which can explain the physics as to why the filters work. I was thinking that the molecules which make up the filter would absorb at a very selective range. But then why wouldn't one get 'light contamination' from the Raman scattering due to the filter itself? How is this avoided or is the filter in some way immune to the Raman scattering effect? I assume this can only be explained with QM but if it can be explained more simply I would welcome that response as well.

Edit: I had this question after watching this video https://www.youtube.com/watch?v=tRrOdKW06sk . If the notch filter is an interference filter as suggested in the comments, the semantics of the question changes to encompass that of interference filters. What is actually occurring at the atomic level so that the angle at which the incident light strikes the filter determines its ability to pass through the filter? Is this due to crystal structure possibly? Why does this angle affect transmittance vs. reflection? And finally why will the laser still only allow one specific wavelength to transmit?

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  • $\begingroup$ (guessing) A lens system that focuses only light scattered from the sample position? Also if the filter is always there, substract a background spectrum? $\endgroup$ – Karl May 11 '18 at 19:14
  • $\begingroup$ Can you post a schematic (or link to one) that shows this filter? $\endgroup$ – Karl May 11 '18 at 19:16
  • $\begingroup$ this reference has a image of a general schematic chm.bris.ac.uk/pt/diamond/stuthesis/chapter2.htm Here is another researchgate.net/figure/… $\endgroup$ – Joe May 11 '18 at 19:20
  • $\begingroup$ that's an interference filter tilted to the exact angle at which it reflects the laser line. No absorption. Plus there are some optical components missing in the schematic imo. Light scattered at the filter would not be focused on the detector. $\endgroup$ – Karl May 11 '18 at 19:28
  • $\begingroup$ Polarization helps also. And comb filters can be used. $\endgroup$ – Jon Custer May 12 '18 at 2:40

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