Forty Years of History of a Grating Interferometer
The present paper deals with the development of studies concerning the employment of diffraction gratings as interferometers, starting in 1922 when they were used to test optical systems. After reporting how a concave surface was tested by means of gratings their elementary theory is described. The phenomenon is further studied from the interferential standpoint and a wave theory of shadows formulated which is analogous to Abbe’s theory on images. A series of studies follows demonstrating that interferential theory accounts for the form of the fringes recorded when a grating is placed on the path of a wave affected by any aberration. In conclusion some simple rules are derived which allow evaluation of both the quality and the amount of the aberration of the wave under test on the basis of the form of the fringes. The sensitivity of the method is then studied, and the most recent developments and better-known applications of the gratings reported concerning their employment as achromatic interferometers.