Phase evaluation of speckle patterns during continuous deformation by use of phase-shifting speckle interferometry

A method for measurement of continuous displacements that uses phase-shifting speckle interferometry is presented. The initial random phase of the speckle pattern is evaluated by phase shifting before deformation. The changing phase thereafter is evaluated from only one image at a time by a least-squares algorithm. The technique can be used for measuring transients and other dynamic events, heat expansion as well as other phenomena, for which it is difficult to accomplish phase shifting during deformation. Theory along with computer simulations and experimental results are described.