What are the key characteristics of notch filters?
Center wavelength (λ₀): the wavelength to be suppressed (e.g. 532nm laser corresponds to a trapped wave).
Bandwidth (Δλ): the range of suppressed wavelengths (narrowband type can be <1nm, broadband type >50nm).
Optical Density (OD): the degree of attenuation of the resistive band (OD4 means transmittance ≤ 0.01%).
Angular sensitivity: changes in the angle of incidence may lead to a shift in the resistive band (thin film type is more sensitive).

What are the applications of notch filters?
Biomedical: elimination of excitation light noise and enhancement of weak signal detection in fluorescence microscopy.
Industrial laser: stray light filtering in LIDAR, precision machining to protect sensors.
Scientific research instruments: Raman spectroscopy, astronomical observation of the background light suppression, enhance the signal-to-noise ratio.