Laser and White-Light Speckle Techniques: A Tutorial Review
This instructional review begins with descriptions of simple experiments that illustrate the phenomenon of coherent-light speckle and its properties that cause it to be useful for measurement of displacements and strains, namely the sensitivity of speckle brightness to object motion and the relationship between speckle size and imaging aperture. The concepts of laser speckle interferometry, speckle shearography, speckle photography, and white-light speckle photography are presented, and basic apparatus setups for implementation are illustrated. Exceptional data density and flexible displacement sensitivities cause these techniques to be favored for whole-field non-contacting measurements of displacement, strain, and vibrations, as well as for nondestructive inspection. The concept of using phase shifting to increase the precision of speckle interferometry far beyond that offered by analyzing fringe patterns is presented along with details of one method of execution. A simple MATLAB® code for phase-shifting interferometry is included. Illustrative and suggestive applications are drawn from studies in geomechanics, biomechanics, fluid mechanics, NDI, strain analysis, residual stresses, and vibration characterization.