Focusing Efficiency and Resolution of a Nickel Phase Zone Plate for Soft X-rays

A nickel phase zone plate and a gold Fresnel zone plate were experimentally examined in terms of focusing efficiency and spatial resolution in the soft X-ray region. The focusing efficiencies were obtained at wavelengths of 1.8, 2.34, and 5 nm with various monochromaticities. A computer simulation of the focusing efficiency was also performed. A discrepancy was found between these experimental and simulated results at 2.34 nm, indicating that the thickness of the phase zone plate was 75% of the designed thickness or that the optical constants of the actual phase zone plate were 75% of the nickel's optical constants listed in the literature and used for the computer simulation. Spatial resolution obtained at 1.8 nm varied slightly with varying monochromaticity of the incident X-ray; the better monochromaticity gave the better resolution.