Generalizing variable shear interferometry for the study of stationary and moving refractive index fields with the use of laser light

Abstract

Instead of adapting existing optical systems for use with laser sources, the additional facilities offered by coherent light have been used as the starting-point for designing a new kind of variable shear interferometer capable also of infinite fringe operation and velocity measurement. At the same time the theory of interference has been generalized to cover variable shear, double exposure and Doppler shift techniques. The practical result is a device which differs from a conventional schlieren system only by the addition of a grating, which can be produced as a hologram, and of various stops. Velocity measurement involves the use of a photodetector and associated display equipment in the same system. The large variety of methods have been applied, by way of illustration, to several different phase objects using beam diameters up to 50 cm.