Grazing-incidence diffraction on $\mathrm{LiNbO_3}$ under surface acoustic wave excitation

X-ray diffraction under grazing incidence and exit angles,αi andαf (GII) was used for the first time to study longitudinal displacements in surface acoustic waves (SAW) propagating on LiNbO3 single crystals. Theαf-resolved (006)-diffraction spectra have been investigated as a function of the applied voltage for SAW excitation. Substantial increase of diffraction intensity (up to 100%), accompanied by a sharpening of the diffraction profile was found in these measurements. The most pronounced influence of SAW on GID was observed for both theαi andαf near the critical angleαc. The diffraction rods were successfully simulated in the framework of dynamical diffraction theory, using only one SAW-related parameter, namely an additional Debye-Waller factor responsible for reduction of the scattering amplitude. This heuristic approach allowed to explain all experimental effects and served to estimate the amplitudes of the longitudinal component of the SAW in the near-surface layer of LiNbO3