INTERACTION BETWEEN X-RAYS AND SURFACE ACOUSTIC WAVES : APPLICATION TO THE SPACE-TIME MODULATION OF AN X-RAY BEAM Michel Brunel¹, D. Roshchupkin^1,2, I. Schelokov^1,2, R. Tucoulou¹

1-Laboratoire de cristallographie,CNRS,BP166, 38042 Grenoble, cedex 09

2- IMT, 142432 Chernogolovka, Moscow District, Russia

The reflection of an X-ray beam ([[lambda]]~1 Å) on a piezoelectric crystal excited by surface acoustic waves produces satellite peaks on both sides of the reflected beam.

We showed that : The angular position of these peaks can be moved by changing the acoustic frequency (around the resonance frequency of the emitter). This is a way of performing an electronic space scanning of an X-ray beam. It is possible to obtain a scan of 1 mm at 1 meter from the crystal with a resolution of the order of 1 Å. Unfortunately, up to now, the minimum width of X-ray beams obtained with Bragg-Fresnel lenses is about 1 um. Nevertheless, the coupling of these two systems gives some encouraging results on the space scanning of a focused X-ray beam.

It has been shown that the coupling of two surface acoustic wave devices in a Kirkpatrick-Baez scheme provides a way of performing an X-Y scan.

A time modulation of the satellite intensities can be obtained by modulating the surface acoustic wave. The shortest X-ray pulses obtained for a beam width of 10 um is of the order of 0.1 us with an efficiency in terms of intensity reaching 50 % of the direct beam. For this, it is necessary to coat a multilayer on the piezoelectric substrate in order to use Bragg diffraction. The time range of these X pulses strongly depends on the time required by the acoustic pulses to cross the irradiated area. This effect can be used to design a high-frequency X-ray beam chopper for time resolved experiments on synchrotrons.

Some memory effects (~ 30 min) occur when a stationary acoustic wave and an X-ray beam interact on the surface of the piezoelectric crystal. This is certainly due to a periodic repartition of charges created by the ionization of the material under the X-ray irradiation.