Blocker
A blocker is a filter that attenuates ("blocks") in the off-band spectral ranges of a bandpass, i.e. attenuates a certain area of the spectrum. They are used to prevent undesirable components of the wavelength spectrum or light radiation. For this purpose, a thin-film interference coating is installed in a bandpass filter to extend the exclusion area of the primary coating in the filter. A blocker is usually a very broadband bandpass filter with high transmission in the passband of the primary filter.
