Uncertainty evaluation of displacements measured by electronic speckle-pattern interferometry

We have applied electronic speckle-pattern interferometry (ESPI), a whole-field optical technique, to measure the displacements induced by applying tensile load on a metallic sheet sample. Because we used a dual-beam ESPI interferometer with collimated incident beams, our measurements were affected by errors in the collimation and in the alignment of the illuminating beams of the optical setup. In this paper, the influences of these errors are characterized and compared with other systematic effects through an uncertainty analysis. We found that the displacement uncertainty depends strongly on the incidence angles of the illuminating beams of the interferometer. Moreover, faults in the alignment of the incident beams have more influence on the uncertainty than errors in their collimation. The latter errors change the incident beams from collimated to slightly divergent, modifying in turn the interferometer sensitivity. We found that this sensitivity change can be generally neglected.