Theory of the erdmann interferometer for investigation of compressible flows

Summary

A theory is developed which allows the calculation of the intensity at the image when phase differences at the object are made visible by the field-absorption method. The resulting formulae have been applied to some particular density fields (differences in phase being proportional to differences in density), viz. to a rectangular object of constant density, a similar object with linearly increasing intensity and a square object with linearly increasing intensity along a diagonal. The narrow interference slit is assumed to be infinitely long and is perpendicular to the gradient of the density for the examples presented. The results are in excellent agreement with experiments and confirm that the optical distance between the dark lines at the image corresponds to one wavelength at the object.