Profile- and deformation-measurements with high axial resolution using the acoustical holography

An improved acoustic-holographic reconstruction-algorithm is presented which allows a three-dimensional image-reconstruction, together with - for the first time - an axial resolution much below one wavelength. This high resolution makes it possible not only to evaluate exactly the contours of defects in the axial direction but also to measure its deformation under thermal or mechanical load. Experimental measurements correspond to the theoretical model, being limited primarily by the dynamic range of the experimental setup. (orig.)