Diffracting aperture based differential phase contrast for scanning X-ray microscopy

Abstract

It is demonstrated that in a zone plate based scanning X-ray microscope, used to image low absorbing, heterogeneous matter at a mesoscopic scale, differential phase contrast (DPC) can be implemented without adding any additional optical component to the normal scheme of the microscope. The DPC mode is simply generated by an appropriate positioning and alignment of microscope apertures. Diffraction from the apertures produces a wave front with a non-uniform intensity. The signal recorded by a pinhole photo diode located in the intensity gradient is highly sensitive to phase changes introduced by the specimen to be recorded. The feasibility of this novel DPC technique was proven with the scanning X-ray microscope at the ID21 beamline of the European Synchrotron Radiation facility (ESRF) operated at 6 keV photon energy. We observe a differential phase contrast, similar to Nomarski's differential interference contrast for the light microscope, which results in a tremendous increase in image contrast of up to 20 % when imaging low absorbing specimen.

Simultaneous cryo X-ray ptychographic and fluorescence microscopy of green algae

“…However, XFM does not usually show much cellular ultrastructure, because the light elements (such as H, C, N, and O, which are the main constituents of biological materials) have low fluorescence yield (4). At the multi-keV X-ray energies needed to excite most X-ray fluorescence lines of interest, these light elements show little absorption contrast, but phase contrast can be used to image cellular structure (5,6) and this can be combined with scanned-beam XFM (7)(8)(9)(10)(11).…”

Quantitative amplitude and phase contrast imaging in a scanning transmission X-ray microscope

“…(12) For Eq. (18) to be valid, the noise power has to be equal for opposing detector segments. For the zero frequency component, we assume that the noise contribution is negligible (i.e., the noise has an average close to zero) and that H r ðf ¼ 0Þ is small compared to the Dirac D-term in Eq.…”

“…However, there have been fewer demonstrations of phase contrast imaging in STXMs because in most cases a large area X-ray detector has been used to measure the transmitted signal. Previous work in phase contrast imaging in STXM includes the use of configured detectors [13,14], a wavefront profiler in combination with a slit detector [15][16][17], aperture alignment [18], and the use of offset zone plate (ZP) doublets [19]. The work described here [20] also uses a configured detector, with an emphasis on obtaining quantitative phase contrast images.…”

Synchrotron X-Ray Microfluorescence and Microspectroscopy: Application and Perspectives in Materials Science

“…Due to the relative magnitudes of the real (phase-shifting) and imaginary (absorption) parts of the refractive index for materials, the use of phase contrast techniques can often lead to a tremendous reduction of the X-ray dose applied to the specimen [15]. Three original strategies are currently employed on ID21: differential phase contrast (DPC) using configured detectors on the SXM proposed by G. Morrison et al [16], differential interferential contrast (DIC) with a configured zone plate on both SXM and TXM [17,18], and finally, Zernike X-ray microscopy, which has been successfully developed on the TXM. As proposed by Zernike for visible light microscopy, phase contrast images are obtained in a full-field microscope by inserting a phase plate in the back focal plane of the objective [19].…”