New shearography: theory, experiments, and some applications

The paper discusses the theoretical and experimental justification and some applications of new shearography, which is two orders of magnitude higher in sensitivity and spatial resolution than the previously known version of shearography. In addition, it has no such negative properties of the old shearography as low contrast of correlation bands and their disappearance with the slightest translational motion of the object of diagnostics. It is shown that a new mechano-optical effect is the physical basis of the method. Due to this effect, the shearing interference of waves occurs spontaneously, without using special optics. Formulas are given that relate the parameters characterizing the translational motion of an object, the average value, dispersion, time autocorrelation and spectral functions of object deformations to the speckle dynamics parameters in the object image plane. These formulas were found both for a light-scattering surface and for a transparent object located near a random-phase screen. It is also shown that, if the difference in the optical paths u of two waves is equal to the sum of M independent values of um, it becomes possible to determine the above parameters corresponding to the terms um, m = 1, 2, ... M. The results of applying the theory to the study of irreversible processes caused by fatigue of materials, intracellular processes in cultured living cells, and turbulent flows are shown. Fatigue-induced degradation mechanisms identified by the new method for some materials are considered. A decrease in cell activity when three toxic substances are introduced into a nutrient solution is evaluated, as well as the relative contribution of vortices with different relaxation times to a turbulent air flow.