Shearography technology is laser measurement method and derivate of a conventional electronic interferometric speckle measurement method (ESPI). This adaptation of Shearography enables the use in field under non-vibration isolated conditions enjoying still the high measurement sensitivity that Laser-Shearography provides to the end-user of 30nm out-of-plane (z-direction).
The Shearography sensor illuminates the surface with speckled laser light emitted from the laser diodes. The reflection of the laser light carries the surface information to the observing CCD camera. Shearography always needs a reference image and a loading image of a component for measurement results. Exposed to load (thermal heat pulse, vacuum, etc.) the inspected material shows a local deformation (loading image). From the loading image the reference is subtracted. The local defect shows a different behavior exposed to load than its surrounding healthy area.
Since Shearography is a differential measurement method with sheared object beams, which ensures system stability for use in field. Not the deformation of the defect is detected but the gradient of the deformation. Therefore typical Shearography defects images show the butterfly defect that is seen in the animation below.