Detection of undersampling from measured phase-shifting data

A method is discussed to free the phase-unwrapping procedure of phase-shifting interferometry from ambiguities introduced by undetected violations of the sampling theorem. From the measured data the visibility of the interference pattern can be calculated and is used as a criterion for such violations. In a real interferometer this visibility tends to local variations with the phase to be measured because of reference phase errors and other influences. Here we discuss methods to get rid of the most serious disturbances and to establish a more reliable masking criterion.