Electronic Speckle Photography: Some Applications

A diffusely reflecting surface illuminated by coherent (laser) light appears grainy when viewed by eye or by a camera. These so called laser speckles form a pattern which behaves as being attached to the surface. They follow any surface displacement. This property is the basis for the measurement of in-plane displacement fields by speckle photography1. By recording two images of the surface, one before and one after a deformation, two speckle patterns will be recorded. The displacement of a point on the surface is obtained from the displacement of the corresponding speckles in the two speckle images. A similar approach is to cover the surface to be studied with a synthetic pattern and use white light for illumination. The analysis of the two techniques are identical. In this paper three experiments using a newly developed electronic speckle photography system are presented.