Low-energy x-ray microscopy with user-defined resolution
Our phase-sensitive methods use absorbing masks with apertures to make an x-ray imaging system sensitive to refraction and ultra-small angle scattering. An additional advantage of an apertured pre-sample masks is that it allows achieving a resolution determined purely by the size of the apertures. These are typically regularly spaced, and since the sample parts corresponding to areas between adjacent apertures are not illuminated during an x-ray shot, they do not contribute to the image; their contribution can be recovered in subsequent shots by displacing the sample or the mask. This means the system resolution can be determined by the user by selecting a given aperture size. We exploited this property in combination with micron-size apertures to realise a laboratory-based microscopy system, using low x-ray energy (the Cu Ka line at ~8 keV) for maximum sensitivity to soft biological tissues. Coupled with a detector with a pixel size smaller than the mask period, this allows the simultaneous retrieval of attenuation, phase and dark-field images from a single image. Notably, since the latter image is sensitive to sub-resolution sample features, pushing the resolution down to the micron level makes dark-field sensitive to structures on the nanometric scale.
Attenuation (top), differential phase (middle) and dark-field (bottom) images of a bar pattern test object, extracted from the same dataset acquired with the laboratory-based low-energy x-ray microscope. The bars in the pattern on the far right are 1 micron in size.