Stepped-amplitude modulation interferometry a new real-time mechanical vibrations measurement technique

The iso-amplitude fringe patterns obtained by real-time time-average electronic holography may have high densities in some regions of the object, and fringe contrast is strongly decreasing with increasing fringe order due to the Bessel-type distribution of brightness. The quantitative interpretation is then prohibited by the poor spatial resolution due to electronic and speckle noise, and by the low fringe contrast in the displayed image The new interferometric technique eliminates these limiting factors. It consists in computing and displaying in real-time a quasi-binary interferometric image with a high fringe contrast which is constant for any fringe order, and with a fringe spacing doubled with respect to previous methods, extending the measurement range by a factor of two.