X-ray imaging microscope with a partial coherent illumination

An x-ray imaging microscopy experiment was performed at the x-ray energy of 8 keV. A Fresnel zone plate (FZP) fabricated by electron-beam lithography technique was used as an objective. Material of the zone structure is tantalum. The experiment was done at the undulator beamline BL47XU of SPring-8. Undulator radiation was monochromatized by passing through a liquid nitrogen cooled Si 111 double crystal monochromator. In order to eliminate speckle-like background noise, a partial coherent illumination was introduced by using a "beam diffuser" consisted of graphite powder. Beam spread of the illumination with the diffuser was about 35 μrad. A charge coupled device (CCD) camera coupled with a phosphor screen and a microscope objective (× 12 or × 24) was used as an image detector. Converted pixel size with the × 24 lens was 0.5 μm. Magnification of the x-ray microscope system was set to be 7.61 - 13. Pitch of 0.6 μm (0.3 μm line and 0.3 μm space) pattern of the test chart was resolved, and the outermost zone structure of the same type of FZP was observed. Imaging properties are also discussed by using Hopkins' optical imaging theory.