| Notch filters, also commonly referred to as band-stop or band-rejection filters, transmit most wavelengths with virtually no intensity loss, while attenuating light within a specific wavelength range (stop band) to very low levels . In fact, they are the exact opposite of bandpass filters, which have high transmittance in the bandpass range and high rejection outside the bandpass range, and thus transmit only a very small range of wavelengths. Notch filters are useful for applications that require filtering out light emitted by a laser. For example, in Raman spectroscopy experiments, it is crucial to suppress the pump laser in order to obtain a good signal-to-noise ratio. This can be achieved by placing a notch filter on the detection channel. In addition to spectrometers, notch filters are frequently used in laser-based fluorescence instruments and biomedical laser systems. |
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