Coherence Studies at the New Transmission Full-Field X-ray Microscope at BESSY GmbH
Brittany Marie McClinton and Weilun Chao1
National Science Foundation 0310717
In order to produce high-fidelity imaging with accurate information about an object of interest, the quantitative relationship between an object and its image must be fully understood. It is not sufficient to know only the light-transmitting, reflecting, or emitting properties of both the object and the imaging system. The coherence properties of the system must also be well characterized, for they have a significant influence on the image ultimately observed. At the synchrotron BESSY GmbH in Berlin--a third-generation light source--a new transmission X-ray microscope at the undulator beamline U41 has just been developed. Using an incorporated high-resolution light microscope, the new instrument is capable of correlative light and X-ray microscopy as well as spectromicroscopy with polarized X-rays from a helical undulator with E/ΔE = 104. The summer of 2008 was spent characterizing the partial coherent properties of the illumination of the system.
By comparing contrast-through-focus experimental data of gratings to simulations based on the 4-dimensional Hopkins equation for the propagation of the mutual coherence, the value of sigma for partial coherence in the object plane can be extrapolated. The variable space includes shaking (scan through angle or at a fixed position), energy, monochromaticity, as well as numerous orientations of linear gratings, circular gratings, and elbows. Nearly 1500 images were taken and data analysis continues.
Figure 1: A circular grating -10 µm out of focus with a 40 nm microzoneplate objective at an energy of 520 eV. The persisting presence of the image of the grating suggests high coherence of the light source.
1CXRO - LBNL