Measurement of absolute three-dimensional displacement gradients using tri-color quad-beam digital shearography

A tri-color quad-beam digital shearography is proposed to achieve the measurement of absolute three-dimensional (3D) displacement gradients. Four laser beams with three different center wavelengths are symmetrically irradiated to the object surface from the upper and lower left and right directions. Four phase maps are then extracted from the two interferograms obtained from two shots. Based on these four phase maps, the absolute 3D displacement gradients are determined. This means of absolute 3D displacement gradient measurement effectively improves the measurement capability of digital shearography and expands its application range.