Post-processing of a focused-image hologram in the digital holographic interferometry

Methods of contrast increasing of the interference patterns in digital holographic interferometry by numerical linear phase modulation and interpolation post-processing of digital focused-image holograms are discussed. It is shown that the linear phase modulation of the hologram leads to a shift of the object field spatial spectrum, whereas the step-in-interpolation procedure of the holograms leads to a broader spatial spectrum of the hologram. In both cases it becomes possible to separate an extended frequency range of the restored object field and, thus, significantly reduce the speckle size in the reconstructed object image, also increasing the fringe contrast in the holographic interferograms. The effectiveness of the methods is shown for holographic interferograms of the elastic deformation of a metallic membrane that is rigidly fixed on the contour.