Surface profiling using shearography

Abstract

We review profile measurement methods using shearography. Traditionally, shearography implies the use of small image shearing, which yields first-order derivatives of displacements or of spatial coordinates. We demonstrate that the use of large image shearing is equivalent to holography, since displacement-related, or spatial coordinate-related, phase fringes are generated. Hence, the technique of shearography can appropriately be perceived as an optical technique that directly measures displacements (or spatial coordinates) and surface strains (or surface slopes). Unlike holography, shearography does not require special vibration isolation since a separate reference beam is not required; hence, it is a practical tool that can be used in the field/factory environment. Examples of the use of small and large image shearing for surface profiling are given. Finally, a novel method for computing phase derivatives for the determination of curvatures of object surfaces from shearographic measurements is discussed.