Very Accurate Measurement of Fringe Shifts in an Optical Interferometer Study of Gas Flow

Abstract

A new means of measuring fringe shifts for certain types of interferograms has been devised, and experimental tests indicate that accuracy of better than one five‐hundreth of the fringe separation is possible. The method and tests of its accuracy for a simple case of parallel fringes are described. The method eliminates concern over refraction effects in interferograms of a class of gas flows. Among certain measurements with the interferometer which are expected to be greatly facilitated by use of this technique, is the measurement of the density distribution within a low density shock wave front. Some other applications are suggested.