Hybrid optical and electronic image processing for strain measurements by speckle photography

A Young's fringe processor for speckle photographs is described. It automatically measures fringe separation and orientation with an accuracy of 1% and 1°, respectively. The fringe evaluation is fast and computer controlled. Fringe densities of one to twenty fringes within the diffraction pattern can be treated with the same resolution. Application to displacement and strain measurements by focused image speckle photography is reported. Local strains can be determined with an accuracy of ∼∊ = 10−5 for displacements between 10 and 100 μm and a spatial resolution of 10 mm.