EXPERIMENTS IN SOFT X-RAY NEAR-FIELD DIFFRACTION IMAGING WITH AN UNDULATOR.

Experiments on soft X-ray near-field diffraction imaging and holography have been carried out with 25-angstrom and 36-angstrom undulator radiation at the National Synchrotron Light Source. By using a near-field version of the Gabor hologram geometry, the experimenters are attempting to capitalize on the high spatial resolution offered by PMMA and a copolymer of PMMA/MAA photoresist detectors. They plan to numerically reconstruct the image from a high-resolution map of the detected exposure level made by electron microscopy or some other means. They are considering reconstruction either along the lines of classical holography or by phasing the diffraction field through use of the multiple near-field recordings. The technique requires coherent illumination of the sample and the entire recording areas, which puts severe demands on the brightness of the source. By using an undulator and diffraction grating monochromator with a resolving power of lambda / DELTA lambda congruent 500, a spatially and temporally coherent X-ray flux of 2 multiplied by 10**8 photons/s was obtained. Contact images and holograms of both test objects and biological samples have been made; the best recordings made so far have been of biological samples.