Fabry–Pérot interferometer

The Fabry -Perot interferometer, and Fabry-Perot interferometer was developed in 1897 by the French physicists Charles Fabry and Alfred Perot. It consists of an optical resonator, which is formed from two partially transparent mirrors. If the mirror spacing invariable (eg, glass with the vapor-deposited mirrors ), these structures are used as a measuring standard, and then referred to as Fabry-Perot etalon. An incoming light beam is only passed through this structure ( transmitted ) as it corresponds to a resonant condition. This allows the Fabry -Perot interferometer, inter alia, to use as an optical filter, which filters out a narrow-band spectrum of a broad-band radiation. Mirror shifts also allow a change of the transmitted radiation. The transmission behavior can be combined with the Airy formula to calculate.

Operation

The Fabry -Perot interferometer is composed of two semi-reflecting mirrors of high reflectivity, which together form an optical resonator. The transmission spectrum of this arrangement shows narrow transmission maxima for wavelengths that satisfy the resonance condition, while other spectral regions are almost completely wiped out in the transmission. This is done by constructive or destructive interference of the partial beams. The distance of the transmission peaks is called free spectral range of the resonator. The frequency separation distance is from the mirror and the refractive index depending on:

The so-called finesse used to characterize the resonator. It is defined as the ratio between the free spectral range and the half- width of a single peak:

The greater the finesse, the more radiation beam interfere with each other and thus the sharper the interference rings. Simple Fabry -Perot interferometer achieve visible light finesse of about. At high reflectivity R of the mirrors and with low attenuation in the resonator finesse assumes large values.

With dielectric thin overlays and curved mirrors to make refinements to reach. With increasing fineness increases in response to the intensity or field strength of the light waves within the interferometer resonator, or to levels which are substantially higher than those of the passing light. This fact must be in applications where the performance is at the forefront, into account ( for example, in laser resonators, and modulators ).

The resonance peaks are the longitudinal modes of a laser. Depending on the gain bandwidth it can oscillate on one or more of these modes or " lasers ".

Diameter of the interference fringes

If one (1) used in (2 ) is obtained with optical path difference is between the reflected rays. This yields the maximum order of the Rings, for a solid:

The innermost ring belongs to the order, so be ready with (4) and ( 3) the angle given. It then calculates the diameter of the innermost ring when one considers that the maximum angle of incidence of the light rays is assumed equal to 0 (normal incidence ). Thus, the diameter of the innermost ring is given by:

Applications

Applies the Fabry -Perot interferometer:

• In spectroscopy as a tunable interference filter or to calibrate an unknown or non-linear frequency scale.
• In a modified form in the research as virtually imaged phased array for spectrometric applications or in communications technology for wavelength division multiplexing
• As a mechanical modulator for monochromatic radiation, such as a CO2 laser at a wavelength of 10.6 microns ( modulated beam power up to 100 watts)
• A laser cavity
• In astronomy: in the H -alpha telescope to observe the Sun