On peculiarities of X-ray diffraction on a surface acoustic wave in grazing geometry

The problem of X-ray diffraction on surface acoustic wave, when the incident and diffracted beams form small grazing angles with the crystal surface as compared with critical angle is considered. It is assumed that the displacement vector of oscillating atoms u is directed with regard to the diffraction vector h so that |hu| << 1, i.e. the considered displacements do not cause any deviation from the Bragg condition, but cause changes in the microrelief of crystal surface. It is shown that the diffracted beams form a caustic surface with time-averaged position deviated with respect to position without acoustic wave, and the value of deviation depends on the amplitude of surface acoustic wave. A possibility of determination of the surface acoustic wave amplitude is discussed