Theory and Application of Point-Diffraction Interferometers

The point-diffraction interferometer is an interferometer for measuring phase variations in which the reference wave is produced by a point discontinuity in the path of the beam. Its simplicity makes it very suitable for testing instruments in situ, and some such tests are described. The general theory shows that other diffracting apertures can be used and relates the technique to phase-contrast microscopy and to scatter-plate interferometry.