Strain analysis by one-beam laser speckle interferometry. 1: Single aperture method.

A two-dimensional analysis of a double-exposed speckle pattern as created by illuminating a plane surface with a beam of laser light is presented with the role played by the aperture illumination function described in detail. Between exposures, the surface is to undergo in-plane general deformation. Two approaches (one whole field and one pointwise) are presented to delineate from the speckle pattern the three Cartesian components of strain at each point in the field. An analogy is drawn between the whole field approach and the classical in-plane moiré method. Quantitative examples are included to demonstrate the validity of the methods.