Direct measurement of rotation by a laser speckle method

Abstract

The laser speckle pattern produced by the coherent illumination of a small circular portion of a doubly exposed photograph contains enough information to reveal not only the displacement but also the rotation of a rigidly moving two-dimensional field. The displacement of the field is contained in the resulting parallel speckle fringe spacing in the usual way. The magnitude of the rotation of the field, however, may be determined by measuring the radius of the circular region within which these displacement speckle fringes appear.Photographs and analyses of the resulting speckle patterns are presented. Non-rigid two-dimensional motion and its relation to incompressible fluid flow is also disc..