In optics, a
Fabry-Perot etalon (or interferometer) is typically made of two
parallel highly-reflecting plates. Its transmission
spectrum as a function of
wavelength exhibits peaks of large transmission corresponding to resonances of the etalon.
The basic characteristics of a Fabry-Perot etalon are:
- the reflectivity R of the plates (mirrors)
- the distance D between the plates
- the index of refraction n of the medium in between the plates
The fundamental properties of a Fabry-Perot etalon are:
- the free spectral range[?] (FSR), which is the wavelength separation between two consecutive transmission peaks
- FSR = c/(2nL), where c is the speed of light
- the full-width at half-maximum (FWHM) of a transmission peak
- the finesse F = FSR / FWHM
A Fabry-Perot interferometer differs from a Fabry-Perot etalon in the fact that
the distance D between the plates can be tuned in order to change the wavelengths
at which transmission peaks occur.
Fabry-Perot interferometers or etalons are used in spectroscopy, lasers, and astronomy.