Strain imaging in thermoelectric devices by laser probe shearography

We have developed an original optical set-up and method for the measurement of strain in electronic components. We have applied it for the study of thermoelectric devices. The method is based on speckle interferometry imaging called shearography. Two images of a same object lighted by coherent laser light are recorded upon a CCD camera through an appropriate optical system. The two images are slightly shifted one with respect to the other. This allows determining the gradient of normal surface displacement in the direction of the shift. Information taken in this manner in several directions allows to derive a map of a parameter related to the surface displacement gradients that we call "fragility factor"