Photograph of a <a href="https://en.wikipedia.org/wiki/Fabry%E2%80%93P%C3%A9rot_interferometer" class="extiw" title="w:Fabry–Pérot interferometer">Fabry–Pérot interferometer</a> for laser wavelength scanning applications.
<a href="//commons.wikimedia.org/wiki/User:Geek3" title="User:Geek3">Geek3</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>