Speckle Method for the Measurement of Helical Motion of a Rigid Body

The helical motion of an object having the rotation axis parallel to the axis of the optical system is measured by the double exposure speckle technique. The object is illuminated with a multimode dye laser light, and the amounts of the rotation angle as well as the translation are obtained from the interference fringes modulating the optical Fourier transforms of specific points on the exposed photographic plate.