Relative to the application of laser emission, the notch filter is very important. In the spectrum experiment, in order to obtain a good signal-to-noise ratio, it is very critical to suppress the pump laser. This can be achieved by placing a notch filter on the detection channel. Notch filters are often used in spectrometers, laser-based fluorescence instruments and biomedical laser systems.
   Similar with Dielectric filters, the transmission of the notch filter is related to the angle of incidence. The center wavelength of the stop band region will shift to shorter wavelengths as the angle of incidence increases.