X-RAY COHERENCE AND ULTRA-SMALL ANGLE RESOLUTION AT GRAZING-INCIDENCEAND EXIT ANGLES

We measure the nonspecular x-ray scattering at grazing incidence and e xit angles from a GaAs surface, modulated by an one-dimensional latera l grating of effectively variable periodicity 1 mu m less than or equa l to d less than or equal to 60 mu m. Due to the projection onto the s ample surface, the lateral coherence length is enlarged by a factor of more than 100. The line broadening of the diffraction maxima is used to deduce the number of periods that add up coherently for a given per iod d and given angle of incidence. We demonstrate that the scattering geometry used allows for large coherently illuminated lengths on the sample and ultra small angle resolution of one- or two-dimensional obj ects. Thus structures of mu m size and larger will be accessible by co herent x-ray scattering.