Studies of the influence of average intensity changes in phase shifted interferograms on phase shift histogram distribution

The phase shift histogram provides an easy way of monitoring the amount of spatial variations of the phase shift in the temporal phase shifting (TPS) method for interferogram analysis. Till now skewness and spread in the histogram have been attributed to phase errors due to tilting or uneven motion of the phase shifter, high numerical aperture reference surfaces, additive and multiplicative noises, higher harmonics in the fringes and quantization of intensity values. Our recent work evidences a crucial influence of average intensity changes in component frames on calculated two-beam interferogram contrast mapsencountered in time-average interferometry applied for vibration testing. Computer simulations and experimental results of the studies of the influence of average intensity changes (due to light source power changes or an automatic gain control in the CCD camera) on the shape of the phase shift histograms are presented. Good experimental corroboration of numerical investigations will be shown on the example of testing vibrations of silicon micromembranes with specular reflection surfaces.