While optical plates with spatially varying phase have been used to increase contrast in visible-light microscopy, they can also be used to similar effect in x-ray microscopy. Anne Sakdinawat of the University of California, Berkeley, and Yanwei Liu of Lawrence Berkeley National Laboratory (Berkeley, CA) are using spiral zone plates (SZPs) to simultaneously image and edge-enhance small x-ray-illuminated objects by a radial Hilbert filtering operation.
For test, the researchers created three different zone plates: one with no spiral at all (as a reference); one SZP with a single spiral arm (“charge 1”); and one SZP with two spiral arms (“charge 2”). To fabricate them, gold and chromium films were deposited on a silicon nitride membrane substrate and patterned with electron-beam lithography. An undulator at the Advanced Light Source in Berkeley, along with a monochromator, provided light at 2.73 nm with a spectral bandwidth (δλ/λ) of 1/500. A 1 µm hole served as the object. While the regular zone plate produced a filled-in spot as an image (top), the charge 1 and 2 SZPs created edge-enhanced images, with the charge 2 image being larger (bottom). Contact Sakdinawat at [email protected].