Surface profiling using shearography

We review profile measurement methods using shearography. Traditionally, sh earography implies the use of small image shearing, which yields first-orde r derivatives of displacements or of spatial coordinates. We demonstrate th at the use of large image shearing is equivalent to holography, since displ acement-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 coordin ates) and surface strains (or surface slopes). Unlike holography, shearogra phy 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 th e field/factory environment. Examples of the use of small and large image s hearing for surface profiling are given. Finally, a novel method for comput ing phase derivatives for the determination of curvatures of object surface s from shearographic measurements is discussed. (C) 2000 society of Photo-o ptical Instrumentation Engineers. [S0091-3286(00)00201-4].