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Although the use of white beam stroboscopic topography at synchrotron stations has allowed a good understanding of the propagation of ultra-acoustic waves [1], section topography remains a powerful tool for a quantitative analysis of the deformation induced by the waves [2]. When the deformation increases one may observe different states: firstly the usual extinction fringes are only slightly enlarged, then new fringes appear and progressively become the only visible fringes. Their number is linked to the mode of the excited ultra-acoustic wave. Then the whole image is changed: the fringes are curved and their shape allows to quantitatively measure the shape of the deformation along the surface of the device. At the same time the number of visible fringes decreases. In the present study we will examine by means of experiments performed at synchrotron stations at LURE and at ESRF the different states of the contrast. We will study the transition from weak to important deformations showing the appearance of the new set of fringes. We will show how the fringes in the most deformed areas are linked to the fringes in the less deformed areas, near the edges of the device, where the deformation becomes negligible. Simulations computed in the case of weak and intermediate amplitudes of vibration are in good agreement with the experiments. In the case of important deformations the contrast may be interpreted by means of the kinematical theory only. These experiments demonstrate the interest of an 'old' technique, section topography, used together with a modern one, synchrotron topography, since the resolution achievable with a conventional setting in the laboratory would not permit such a high resolution study of the fringes. References [1] Capelle B., Détaint J, Zarka. A. & Epelboin Y. (1998), Proc. IEEE Int. Freq. Control Symp. 27-29 May 1998, Los Angeles, USA, pp 816-822 [2] B. Capelle, J. Détaint & Y. Epelboin (2001) J. Appl. Cryst., 34, 1-6

Study of the contrast induced by ultra-acoustic waves in piezoelectric devices in stroboscopic X-ray section topographs