Interferometric displacement measurement on scattering surfaces utilizing speckle effect

Abstract

When a surface is illuminated with laser light it has a speckled appearance due to random interference. If two speckle patterns are superimposed the distribution of intensity in the resultant pattern depends on the relative phases of the component patterns. By measuring the correlation between the resultant patterns at two different times a change of relative phase is detected. This leads to a versatile method of measuring either the normal or in-plane components of displacement over the whole of a surface at one time.