File:Fabry Perot Interferometer - basic diagram.svg

Author: User:Stigmatella aurantiaca

Source: Own drawing, created using Inkscape

Description: The heart of the Fabry–Pérot interferometer are a pair of partially silvered glass optical flats spaced several millimeters to centimeters apart with the silvered surfaces facing each other. (Alternatively, a Fabry–Pérot etalon is made of a transparent plate with two reflecting surfaces.) The flats are often made in a wedge shape to prevent the rear surfaces from producing interference fringes and/or the rear surfaces will be given an anti-reflective coating. Illumination is via a diffuse source set at the focal plane of a collimating lens. A focusing lens produces what would be an inverted image of the source if the paired flats were not present; i.e. in the absence of the paired flats, all light emitted from point A passing through the optical system would be focused at point A'. In the accompanying illustration, only one ray emitted from point A on the source is traced. As the ray passes through the paired flats, it is multiply reflected to produce multiple transmitted rays which are collected by the focusing lens and brought to point A' on the screen. The complete interference pattern takes the appearance of a set of concentric rings. The sharpness of the rings depends on the reflectivity of the flats. If the reflectivity is high, resulting in a high Q factor (i.e. high finesse), monochromatic light produces a set of narrow bright rings against a dark background.