Effect of Size and Spectral Purity of Source on Fringe Pattern of the Mach-Zehnder Interferometer

Abstract

In analysis of Mach-Zehnder interferograms taken of the axi-symmetric flows about supersonic projectiles, the question arises whether errors in fringe width occur because of the finite size and non-zero spectral width of the source employed. Under the assumptions that the source is a circular area normal to the axis of the interferometer with spectral intensity function approximated by a gaussian error curve, it is shown that the deviations from ideal fringe width λ0/ε caused by source size and spectral line width are negligibly small for an interferogram with 200 fringes on either side of center. The limiting factor is not deviation in fringe width but the exponential damping of fringe intensity amplitude owing to the spectral band width of the source. This reduces the fringe contrast below experimental detectability long before deviations in fringe width become appreciable.