A type of optical filter constructed from a transparent cell containing crushed glass or powder immersed in a specific liquid. It exploits the Christiansen effect to pass a narrow band of wavelengths where the refractive indices of the solid and liquid match, while scattering all other light. Though largely superseded by interference filters, it remains an important concept in optical physics.
Heard on the job
We demonstrated narrow-band transmission in the lab by heating a Christiansen filter to shift its passband.