Real time measurement of very small transverse displacements of diffuse objects by random moiré. 1: Theory.

Illumination of a random diffuse object by a fringe pattern produced by two symmetrical laser beams leads to phenomena that are usually studied with speckle interferometric techniques. We first show that these phenomena are analogous to moiré. We then propose to apply this method for measuring the transverse vibrations of a diffuse surface in real time with interferometric sensitivity. Further, we show that the discussed system can work as a linear displacement transducer; the theoretical aspects of this so-called random moire transducer are investigated.