Scattering of an X-Ray beam on a Surface Acoustic Wave

Abstract

In this work surface acoustic waves (SAWs) are studied as a tool to manipulate spa- tially and temporally an X-ray beam. SAWs have been intensively studied in the last decades, and X-ray diffraction proved to be a useful tool to investigate the propa- gation of a SAW in different materials. A SAW induces a sinusoidal deformation on the substrate surface, which acts as a grating when illuminated by X-rays pro- ducing diffraction satellites. Their intensity and angular separation depend on the amplitude and wavelength of the ultrasonic superlattice. The first two experiment presented in this work studied the spacial manipulation of an X-ray beam. In this case a SAW was excited continuously on the sample. The third and fourth experi- ment used a pulsed SAW to temporally manipulate an X-ray beam. The first experiment studied sagittal diffraction in Bragg condition. It demonstrates that it is possible to achieve an effective diffraction of an X-ray beam in sagittal ge- ometry. The proper theoretical model has been applied for calculation of the SAW amplitude and wavelength. The experimental results and the theoretical predictions show a good agreement. The second experiment investigated for the first time the diffraction of X-rays by a SAW in the soft X-ray region. The results of X-ray Bragg diffraction and total ex- ternal reflection in meridional geometry are analyzed. The possibility to achieve an effective diffraction is demonstrated. The third experiment explored the possibility to electronically manipulate the SAW amplitude, obtaining different scattering conditions for different X-ray pulses. It was performed in quasi-sagittal geometry in Bragg condition. The result of this ex- periment indicates that pulsed SAW can be used to select which X-ray pulse reaches the detector, as long as the X-ray pulses are separated by at least 120 ns. The fourth experiment aimed to study the propagation of pulsed SAW on the sub- strate surface. Individual SAW pulse were localized on the surface. The structure of SAW pulses was investigated and revealed inhomogeneity in the structure. Finally an application is proposed. SAW could be used to develop a pulse picker driven by a SAW, able to pick individual X-ray pulses separated by at least 120 ns.