Narrow band filters transmit only a defined narrow spectral bandwidth. All other wavelengths are blocked or reflected. With our steep-edged filter designs we achieve passbands with bandwidths down to approx. 0.2 nm. We use a monitoring technique that allows us to define the central wavelength (CWL) down to 0.05 nm and at the same time provide transmittance of 98%. In the blocking range, extraneous light is suppressed up to an optical density above >10 by Design without any additional blocking elements.

Narrow-band filters are differentiated between single and multi-cavity designs. The higher the cavity, the steeper the design in combination with a flat passband.
Usually the bandwidth for this variant is defined in the range below 5 nm.

Laser line filters also belong to this group of bandpass filters. Their designs are centered on the wavelengths of common lasers. Background plasma and secondary emissions are suppressed. This improves the signal-to-noise ratio and prevents distortion of the measurement signals.

Depending on the requirement profiles, there are also variants with limited blocking range, such as laser clean-up filters.