Common-Path Interferometer for Testing Purposes

The interferometric method of optical testing presents considerable advantages in view of the unequivocal nature of the information given and the self-calibrating nature of the test. However, difficulties are presented in practical applications of interferometers of the Twyman-Green type because of the necessity of providing a reference beam.Two types of interferometer are described in which the reference beam follows the same path as the test beam, thus avoiding this difficulty. Some test results are given, illustrating a few of the applications of these instruments.