Fabrication and characterization of a condenser zone plate for compact x-ray microscopy

We describe the in-house fabrication and characterization of a condenser zone plate for a compact laser–plasma-based soft x-ray microscope operating at 2.478 nm wavelength. The fabricated condenser has a diameter of 4.53 mm and an outermost zone width of 49 nm. The pattern is generated by a small-write-field e-beam lithography system and 656 single, 100 μm wide write fields are stitched together to obtain the whole pattern. An in-house method based on a laser–plasma source was developed to characterize the condenser zone plate with regards to diffraction efficiency and imaging properties. The measured groove efficiency of the fabricated condenser zone plate was determined to 11%±2% and the imaging properties were found to follow the expectations concerning the object field illumination purpose in the x-ray microscope. The in-house characterization method allows faster process improvement in the small-scale laboratory compared to presently used synchrotron-based methods.