Aberrations of fabry-perot interferometers when used as filters

The spectral and optical performances of Fabry-Perot interferometers having nonuniformities in spacing are discussed, and it is shown that the finesse F of an interferometer with a circular aperture and a parabolic nonuniformity in spacing and that of one with a rectangular aperture and a linear nonuniformity (lack of parallelism) are both given by F = pi {[ (1 - R)(2)/R] + [2pixi/lambda](2)}(-(1/2)), where xi is the maximum nonuniformity across the aperture and R is the plate reflectance. It is also shown that the nonuniformities impair the spectral performance more than the optical, particularly with incident white light.