Digital shearography with in situ phase shift calibration

Precise measurement of the spatial derivative of displacement using digital shearography depends on well-calibrated phase shifts. However, due to time drift or a change in the position of the phase shifter, the previously calibrated results may not be applicable for the measurements. In this paper, we introduce a Michelson-interferometer-based digital shearographic setup, with an in situ phase shift calibration, that precisely measures the displacement derivatives. For the optical arrangement, a small number of optical parts are introduced into the existing Michelson interferometer to carry out the in situ calibration of the phase shifter. The calibration can be carried out anytime without changing the optical arrangement. This feature easily recalibrates the digital shearography, eliminating the influence of the phase shift error.

► We present a digital shearography with in situ phase shift calibration.
► We analyze the error induced by the phase shift error in digital shearography.
► The calibration is realized by optical method rather than statistical methods.
► This shearography achieves the precision measurement of displacement derivatives.