Scanning Differential-Phase-Contrast Hard X-Ray Microscopy with Wedge Absorber Detector

A new and simple idea for scanning differential-phase-contrast (S-DPC) hard X-ray microscopy has been proposed. It only uses a wedge absorber coupled with two intensity detectors, and is much more sensitive to sample structures than absorption contrast. It can also extract pure quantitative one-dimensional phase gradient given by a sample without an effect of sample absorption. The S-DPC microscope has been constructed at BL24XU of SPring-8, and its feasibility has been successfully demonstrated at the photon energy of 10 keV by clearly visualizing structures of samples. Further, the experimental phase gradient profile agrees well with simulation. By integrating the resultant phase gradient, the corresponding phase shift distribution could be also imaged. There are two main types in X-ray microscopes, one is an imaging type and the other is a scanning type. 1) The former provides direct magnification and shorter exposure time, while the latter provides digitally stored images with minimal radiation exposure to samples. 1) Recently, phasecontrast X-ray microscopy has rapidly grown in the hard Xray region since the advent of the 3 rd generation synchrotron radiation facilities. It is based on the fact that phase-shift cross section is almost a thousand times larger than absorption one for light elements as expected from a comparison between real and imaginary parts of the refractive index. 2,3) In the imaging type, the phase-contrast microscopy has been demonstrated by the Zernike's method 6) Further, we have recently demonstrated the novel imaging phase-contrast microscopy using a micro-interferometer consisting of a twin zone plate. 7) On the other hand, in the scanning type, the phase-contrast microscopy has been demonstrated by the configured 8) or segmented 9) detectors, the CCD-camera image-detections, 10-12) the diffracting aperture based method 13) and the dark-field imaging. 14,15) The former two require the highly sophisticated X-ray detector of electronic devises. The CCD-camera imagedetection must take diffraction images of a microbeam for all pixels, thus need a huge memory and the stored dataset must be processed later with an appropriate numerical calculation for image reconstruction. The diffracting aperture based method and the dark-field imaging are simple methods to realize the scanning phase-contrast microscopy, but phase information was not evaluated quantitatively. Here, we propose a new idea for S-DPC hard X-ray microscopy. It is a very simple way to purely extract quantitative one-dimensional phase gradient given by a sample to be imaged removing an effect of sample absorption by only adding a wedge absorber coupled with two intensity detectors into the normal scheme of the scanning microscopy. In this paper, the concept of the S-DPC hard X-ray microscopy is described and the feasibility test is presented. The principle of the S-DPC microscopy is illustrated i