The Christiansen effect occurs when a solid powder is suspended in a liquid, and both materials share the exact same refractive index at a specific wavelength of light. At this matching wavelength, the mixture stops scattering light and becomes highly transparent, acting as a narrow-band optical filter. Outside this wavelength, the differing refractive indices cause the mixture to scatter light and remain opaque.
Heard on the job
We rely on the Christiansen effect in this thermal sensor setup to filter out everything except the target infrared band.
Insider tip
This effect is the working principle behind Christiansen filters, which are valued because they can be tuned by simply changing the temperature of the liquid to shift its refractive index.