Visualization of short surface acoustic waves by stroboscopic x-ray topography: analysis of contrast

Abstract

In this paper the capabilities of stroboscopic x-ray topography to visualize the propagation of short (<10 μm) surface acoustic waves (SAW) in single crystals are analysed. Experiments with LiNbO3 crystals under SAW excitation were carried out at the ID19 beam line of the European synchrotron radiation facility. The developed theoretical analysis of the SAW-induced contrast in Bragg scattering geometry helped to optimize experimental conditions and receive high quality images with well-resolved individual acoustic wave fronts. The basic contrast mechanism is related to the SAW-induced corrugation of atomic planes that causes the focusing of x-rays. The focal distance is directly proportional to the SAW wavelength and inversely proportional to the deformation amplitude at the crystal surface. Simulations of diffraction contrast allowed us to conclude that the best contrast is achieved when the acoustic wave vector is perpendicular to the x-ray scattering plane and the sample/film distance equals 2–4 focal distances.