Gires–Tournois etalon

In optics, a Gires–Tournois etalon (also known as Gires–Tournois interferometer) is a transparent plate with two reflecting surfaces, one of which has very high reflectivity, ideally unity.

Due to multiple-beam interference, light incident on a Gires–Tournois etalon is (almost) completely reflected, but has an effective phase shift that depends strongly on the wavelength of the light.

The complex amplitude reflectivity of a Gires–Tournois etalon is given by where r1 is the complex amplitude reflectivity of the first surface, Suppose that

This indicates that all the incident energy is reflected and intensity is uniform.

However, the multiple reflection causes a nonlinear phase shift

is the intensity reflectivity of the first surface.

Define the effective phase shift

through One obtains For R = 0, no reflection from the first surface and the resultant nonlinear phase shift is equal to the round-trip phase change (

However, as can be seen, when R is increased, the nonlinear phase shift

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

is not observed anymore: the reflectivity starts exhibiting a resonant behavior which is characteristic of Fabry-Pérot etalons.

Schematic of a Gires-Tournois etalon when light impinges at normal incidence on the first reflecting plate.
Nonlinear phase shift Φ as a function of δ for different R values: (a) R = 0, (b) R = 0.1, (c) R = 0.5, and (d) R = 0.9.
Amplitude reflectivity and group delay induced by a Gires-Tournois interferometer with the intensity reflectivity of the first surface being = 0.3 and that of the second surface being =1, i.e. as for a perfect reflector (blue line). In this case the amplitude reflectivity is unity for all frequencies and the resonant behavior of the interferometer is observed only in the imparted group delay. As becomes smaller than 1 (red and green lines), for instance due to losses at the reflector, the Gires-Tournois interferometer starts behaving as a Fabry-Pérot etalon. Other parameters of the calculation are =30 μm, =1 and =0.