What is a notch filter?


A notch filter is an optical filter that blocks incident light within a certain wavelength band. Outside this area it is permeable. It therefore functions in a way that is opposite to the principle of a bandpass filter.

Important for a notch filter are the appropriate blocking band and the actual transmission bands in which the filter is permeable to light. Optical density (OD) is the most widely used unit for the degree of blocking in the blocked area; the higher the optical density, the higher the quality of the notch filter. Notch filters are often used in spectroscopic applications to block light from an excitation laser and only allow the raman signal or fluorescence signal to pass through.

How does a notch filter work?

A notch filter blocks light within a certain wavelength band, while it allows it to pass outside this band.

What are notch filters used for?

Notch filters are used, for example, in spectroscopic applications.

How is a notch filter specified?

A notch filter is characterized by its transmission bands and the blocking band within which the filter is permeable or impermeable. An important quality feature is the optical density in the blocking band.