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In optics, a Fabry–Pérot 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 high surface reflectivities, one may require an extremely high surface quality (low roughness) to realize the theoretically possible finesse. A reduced finesse can also result from using a too small or not properly collimated beam, a too large tilt angle, or a reduced beam quality.
A high finesse is desirable in spectroscopy and spectrum analysis as the Etalon can possess both a large Free Spectral Range and a small resonator bandwidth allowing for a high spectral resolution.
- High-Finesse Resonators For Spectral Analysis
- Apparently Reduced Finesse Due to Higher-Order Modes
- Relation of Finesse to The Q Factor
- More to Learn
An optical resonator with variable length can be used as a tunable frequency filter for spectral analysis: by measuring the optical powerthroughput as a function of resonator length (which is scanned e.g. with a piezo actuator behind one of the mirrors), one can obtain the optical spectrum, provided that it is limited to a region which is smaller t...
Note that the apparent bandwidth of the resonances, observed e.g. by scanning the resonator length while observing the transmission with a single-frequency input wave, can appear to be increased due to the excitation of transverse modes with different orders. For a perfectly aligned confocal resonator, the frequencies of even higher-order modesare ...
The finesse is related to the Q factor: the latter is the finesse times the resonance frequency divided by the free spectral range. Essentially, while the finesse relates the resonance bandwidth to the free spectral range, the Q factor relates it to the average optical frequency. If one increases the resonator's round-trip length while keeping the ...
Encyclopedia articles: 1. cavities 2. Fabry–Perot interferometers 3. supermirrors 4. reference cavities 5. bandwidth
- Spatial mode structure for lowest-order TEM modes. Figure reproduced from Further Development of NICE-OHMs.2.
- Mode spectrum of a Fabry-Pérot interferometer for mirror reflectances of 99.7%, 80%, and 4%, illustrated by a blue, red, and green curve, respectively.
- Schematic of a confocal Fabry-Pérot resonator. Mirrors with radius R=R2 (brown arrows) are separated by a distance L that is equal to the mirror radius.
- Spectrum of a confocal resonator with near perfect spatial mode matching, where every other mode is extinguished as only the fundamental mode is excited.
A Fabry–Pérot interferometer (also called Fabry–Pérot resonator) is a linear optical resonator (or cavity) which consists of two highly reflecting mirrors (with some small transmissivity) and is often used as a high-resolution optical spectrometer.
A high-finesse etalon (red line) shows sharper peaks and lower transmission minima than a low-finesse etalon (blue). A Fabry-Pérot interferometer differs from a Fabry-Pérot etalon in the fact that the distance l between the plates can be tuned in order to change the wavelengths at which transmission peaks occur in the interferometer.
