High precision deformation measurement by digital phase shifting holographic interferometry

A digital phase shifting technique capable of quantitatively determining the phase of holographic interferometric displacement fringes is presented. This technique uses computer control to take data and calculate surface deformation. The phase value at each detector point can be calculated by taking four successive intensity data frames with the reference phase shifted between each frame. The displacement fringe order number can be assigned by adding or subtracting 2 pi from a data point until the phase difference between adjacent data points is less than pi. Experimental results show that this technique can precisely determine a fraction of a fringe with an accuracy of 1 deg.