Electronic heterodyne readout of fringes in moiré deflectometry

An electronic heterodyne technique is described for the readout of fringes in moiré deflectometry. The technique is based on phase measurements of signals generated by a photodetector observing the light transmitted through a traveling moiré fringe pattern. The phase of the signal is proportional to the fringe deviation and thus to the deflection angle of the light ray. The phase is measured on line by a standard phase meter with an accuracy of 1 degrees or 1:360 of a fringe. The technique, which is precise and sensitive, is demonstrated by detecting and measuring a fringe shift of 0.15 mm corresponding to 0.029 of a fringe.