Analysis of mechanical oscillations by speckling.

The application of the speckle phenomenon to the analysis of in-plane translations and oscillations is first reviewed briefly. Then a practical method of investigating out-of-plane rotations (tilts) even in the presence of in-plane movements is studied. This goal can be achieved by recording the speckle patterns in the Fourier transform plane before and after the tilt or as a time-average exposure for an oscillating object. Young's fringes related to the tilts are observed in the Fraunhofer diffraction pattern when the developed photographic plate is illuminated with coherent light. This leads to a very simple engineering tool for the analysis of movements. Theoretical and experimental results will be shown.