Fizeau interferometer in spectral measurements

Abstract

Interferometers used for studies of spectral line profiles should produce instrumentally narrow and smooth interference fringes. We analyze in detail the fringe-formation process in a Fizeau wedge interferometer and develop a fringe-optimization method that can be used to find the optimum angle of incidence for producing the sharpest fringes in the detection plane. We show that the Fizeau fringes can be sharper than generally thought. The Fizeau interferometer can thus be used as a high-resolution spectrum analyzer that is suitable for both pulsed and cw light sources. The spectral resolution of such an analyzer can be made comparable with that of the more common Fabry–Perot interferometer. The Fizeau interferometer, however, does not require the same amount of alignment work and is thus more convenient to use with sources with variable bandwidths. Spectral measurement of pulsed lasers is an important application in which an analyzer of this kind is preferable.