The finest frequency selection may also be obtained through the use of an etalon.

Tresca was also among the designers of the standard metre etalon.

In astronomy an etalon is used to select a single atomic transition for imaging.

It includes etalon polygons on which on-ground and remote information was compared.

In the 18th century this plant was recognized as etalon of Russian Arms Production.

Due to the angle dependence of the transmission, the peaks can also be shifted by rotating the etalon with respect to the beam.

A related device is the Gires-Tournois etalon.

A 'production standard setter (etalon)' aircraft was built in April 1942 with a redesigned engine cowling.

Constructive interference occurs if the transmitted beams are in phase, and this corresponds to a high-transmission peak of the etalon.

The main optical filtering technology used in add-drop multiplexers is the Fabry-Pérot etalon.

In optics, a Gires-Tournois etalon is a transparent plate with two reflecting surfaces, one of which has very high reflectivity.

(Alternatively, a Fabry-Pérot etalon uses a single plate with two parallel reflecting surfaces.)

The varying transmission function of an etalon is caused by interference between the multiple reflections of light between the two reflecting surfaces.

This configuration effectively describes a Fabry-Pérot interferometer or etalon: for , the reflection vanishes.

Gires-Tournois etalon has applications for laser pulse compression and nonlinear Michelson interferometer.

The field coming from Gires-Tournois etalon interferes with the plane field reflected from the ordinary reflector.

A Fabry-Pérot etalon takes advantage of thin film interference to selectively choose which wavelengths of light are allowed to transmit through the device.

(Technically the former is an etalon and the latter is an interferometer, but the terminology is often used inconsistently.)

In the absence of absorption, the reflectance of the etalon R is the complement of the transmittance, such that .

Diesel-engined models in the form of the new Isuzu Bogdan, Tata Etalon and others have seen immense popularity.

Its transmission spectrum as a function of wavelength exhibits peaks of large transmission corresponding to resonances of the etalon.

Without an etalon, a laser will generally produce light over a wavelength range corresponding to a number of cavity modes, which are similar to Fabry-Pérot modes.

A key difference from a Fabry-Perot etalon is that input light that reflects off of the surface of the plate does not contribute to the interference.

Because the phase change from the Gires-Tournois etalon depends on wavelength and shows step-like behavior, nonlinear Michelson interferometer has particular applications.

In the derivation below, n is the index of refraction inside the etalon, and n is that outside the etalon.