Question

what is Fabry-Perot Interferometer?

Answer 1

In optics, a Fabry–Perot interferometer (FPI) or etalon is an optical cavity made from two parallel reflecting surfaces (i.e.: thin mirrors). Optical waves can pass through the optical cavity only when they are in resonance with it.

For more information please visit https://en.wikipedia.org/wiki/Fabry%E2%80%93P%C3%A9rot_interferometer