Composite vibration analysis with modulated electronic speckle shearing interferometry

A video speckle shearing interferometer has been used to study sinusoidally vibrating objects. Theroretical and experimental results show that the shear fringe patterns obtained contour the derivatives of the vibration amplitudes only for pure classical modes and when the shear is small. For composite modes, the fringe patterns observed are more difficult to interpret because the optical phase changes that are contoured are functions of both the spatial derivatives of the vibration amplitude and of the vibration phase.