An in-line shearography setup based on circular polarization gratings

The shearing amount defines the resolution of a speckle shearing interferometer and the shearing direction defines the sensitivity direction of the setup. The properties of circular (cycloid) holographic polarization gratings recorded in liquid crystal polymers can be used to build a new multi-shearing direction and amount shearography setup. The polarization states of the diffracted beams offer an easy way to produce phase shifts and thus to compute the phase contained in the shearograms. The theoretical bases of such a device are highlighted and an original compact and full in-line setup is proposed. First experimental results of delamination detection and flaw detection by shearography are presented. A discussion on the importance of the grating recording and the polarization orientation points out the best working requirements.