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Quantitative measurements of the phase shift of X-rays passing through a matter allow us to perform X-ray phase tomography for visualization of soft materials. Combination of an X-ray microscope and a grating interferometer is a promising approach to realize quantitative phase measurements with a microscopic spatial resolution. A Lau interferometer consisting of a source grating and a phase grating is available for this purpose with an incoherent laboratory X-ray source. We installed a Lau interferometer into a laboratory-based X-ray microscope adopting a copper rotating anode source and Fresnel zone plates (ZEISS Xradia 800 Ultra). A “twin-phase image”, which consists of positive and negative phase images overlaid with a certain separation, is generated through a fringe-scanning measurement with this microscope. A step for generating a quantitative phase image from the twin phase image should be developed to perform phase tomography. However, conventional deconvolution operations are not suitable because of artifacts and noise remained in resultant phase images. To reduce the artifacts and noise, an iterative calculation algorithm has been developed. The evaluation of the algorithm shows that the artifacts and noise are suppressed and quantitative phase images are obtained. Finally, results of phase tomography obtained for soft materials are demonstrated.

X-ray phase tomography by Talbot interferometry functions with X-rays of a broad energy band, and a pink- beam extracted by a multilayer mirror from white synchrotron radiation is used for four-dimensional X-ray phase tomography, which was developed at BL28B2, SPring-8, Japan. Polymer samples under infrared laser irradiation were observed as model experiments of laser processing. In this paper, laser ablation for a carbon-fiber reinforced polymer (CFRP) sample is reported. Thanks to the fact that the fibrous structure generates visibility (or dark-field) contrast, four-dimensional tomogram from the visibility reduction is presented. A technical effort to improve the temporal resolution from 1 s to 160 ms is also described.

X-ray phase/dark-field tomography by using an X-ray grating interferometer and white synchrotron radiation has been demonstrated to observe dynamics in materials consisting of light elements, because it is available with X-rays of a broad energy bandwidth. In this work, we combined X-ray phase/dark-field tomography with a stroboscopic technique, which synchronizes image acquisitions with repetitive tension applied to a sample. Snapshot images with a 200 μs temporal resolution are measured to reconstruct phase/dark-field tomograms. A result of stroboscopic X-ray dark-field tomography is described, which was obtained for a rubber sample under a 24 Hz repetitive compression-stretch motion of a 10 mm amplitude.

This paper review the configurations of grating-based X-ray interferometry for X-ray phase imaging/tomography and describes recent activities for four-dimensional X-ray phase tomography and nanoscopic X-ray phase tomog- raphy. A multilayer mirror to produce a 10% bandwidth pink beam at 25 keV has been installed at SPring-8 for four-dimensional X-ray phase tomography, and an application to polymer laser ablation is presented. A 100-fold full-field X-ray microscope employing a Fresnel zone plate has been used successfully in combination with a Talbot interferometer to perform nanoscopic phase tomography for a malleal processus brevis of a mouse nine days after birth. Another development using a laboratory-based full-field X-ray microscope in combination with a Lau interferometer is also described.

Talbot interferometer using white synchrotron radiation has been demonstrated for time-resolved X-ray phase imaging and tomography as well as four-dimensional phase tomography to observe dynamics in samples. In this study, X-ray phase tomography has been used to follow the time evolution of phase separation in polymer blend through heating treatment. For this purpose, we performed in-situ X-ray phase imaging and tomography with X-ray Talbot-Lau interferometer using white synchrotron radiation. The X-ray Talbot-Lau interferometer consisted of a source grating (30 μm in period), a π/2 phase grating (4.5 μm in period), an amplitude grating (5.3 μm in period) and a high-speed camera. A polymer blend sample of polystyrene (PS) (Mw = 76,500) and polymethyl methacrylate (PMMA) (Mw = 33,200) was used for the CT observation. A compound of the PS and PMMA was made by a twin-screw kneading extruder and put into an Al tube whose inner diameter was 6 mm. The sample temperature was maintained at desired temperature sequence by controlling a lamp for heating, and CT scans were repeated to track the changes in sample structures at a temporal resolution of 5 seconds. PS-rich phase and PMMA-rich phase changing with time evolution were revealed.

An X-ray phase tomographic microscope that can quantitatively measure the refractive index of a sample in three dimensions with a high spatial resolution was developed by installing a Lau interferometer consisting of an absorption grating and a π/2 phase grating into the optics of an X-ray microscope. The optics comprises a Cu rotating anode X-ray source, capillary condenser optics, and a Fresnel zone plate for the objective. The microscope has two optical modes: a large-field-of-view mode (field of view: 65 μm x 65 μm) and a high-resolution mode (spatial resolution: 50 nm). Optimizing the parameters of the interferometer yields a self-image of the phase grating with ~60% visibility. Through the normal fringe-scanning measurement, a twin phase image, which has an overlap of two phase image of opposite contrast with a shear distance much larger than system resolution, is generated. Although artifacts remain to some extent currently when a phase image is calculated from the twin phase image, this system can obtain high-spatial-resolution images resolving 50-nm structures. Phase tomography with this system has also been demonstrated using a phase object.

We have launched a project to promote grating-based X-ray phase imaging/tomography extensively. Here, two main activities are presented for enabling dynamic, or four-dimensional, X-ray phase tomography and nanoscopic X-ray phase tomography by grating interferometry. For the former, while some demonstrations in this direction were performed with white synchrotron radiation, improvement in image quality by spectrum tuning is described. A preliminary result by a total reflection mirror is presented, and as a next step, preparation of a 10% bandpass filter by a multilayer mirror is reported. For the latter, X-ray microscopes available both at synchrotron radiation facilities and laboratories equipped with a Fresnel zone plate are combined with grating interferometry. Here, a preliminary result with a combination of a Lau interferometer and a laboratory-based X-ray microscope is presented.

X-ray nanofocusing devices are capable of focusing X-rays down to sizes of about 10 nm. We have developed a new nanofocusing device, known as total-reflection zone plates (TRZPs), for focusing high-brilliance synchrotron radiation in the hard x-ray region. This device consists of a reflective zone pattern on a flat substrate. It has the potential to focus hard x-rays down to sub-10-nm dimensions. Furthermore, it is considerably easier to fabricate than other hard x-ray nanofocusing devices since it is used with a very small grazing incidence angle. We have focused 10-keV x-rays to sub-15 nm dimensions using a TRZP that was fabricated by conventional electron-beam lithography. In addition, we present designs for more efficient devices that have a target focus size of 5 nm. We propose and discuss a new approach for achieving point focusing with nanometer dimensions.

Point spread functions (PSF) of some kinds of x-ray imaging detectors are directly measured using x-ray microbeam. The experiment has been performed at bending magnet beamline BL20B2 and undulator beamline BL2oXU of Spring-9. The microbeam is focused using a Fresnel zone plate (FZP) with coherent illumination to 0.3micrometers (almost outermost zone width of the FZP). The imaging detectors are put at the focal plane and directly detect the microbeam. Two types of high spatial resolving detectors are tested. One is x-ray- electron conversion type with electro-magnetic lens, and spatial resolution is estimated to 0.7micrometers . The other is x-ray-visible light conversion type with optical lens and the spatial resolution is estimated to 1.0micrometers .

X-ray microbeam using Fresnel zone plate as a beam focusing device has been tested at an undulator beamline of Spring-8. The zone material is tantalum with thickness of 1 micrometers , and the zone structure is fabricated by using electron beam lithography technique. The outermost zone width of the zone plate is 0.25micrometers . By utilizing a fully coherent illumination, a focused spot size near to the diffraction- limit (0.3micrometers ) has been achieved at an X-ray energy of 8 keV. The measured beam profiles shows good agreement with the theoretical profile. The measured diffraction efficiency agrees well with theoretical value within an X- ray energy region from 6 keV to 10 keV. A scanning microscopy experiment has also been performed in order to evaluate the spatial resolution. Fine structures of up to 0.2micrometers are clearly observed in the measured image. The modulation transfer function derived from the measured image is 10% at 0.2micrometers line and 0.2micrometers space.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An x-ray imaging microscopy experiment was performed at the x-ray energy of 8 keV. A Fresnel zone plate (FZP) fabricated by electron-beam lithography technique was used as an objective. Material of the zone structure is tantalum. The experiment was done at the undulator beamline BL47XU of Spring-8. Undulator radiation was monochromatized by passing through a liquid nitrogen cooled Si 111 double crystal monochromator. In order to eliminate speckle-like background noise, a partial coherent illumination was introduced by using a beam diffuser consisted of graphite powder. Beam spread of the illumination with the diffuser was about 35 (mu) rad. A charge coupled device (CCD) camera coupled with a phosphor screen and a microscope objective (x 12 or x 24) was used as an image detector. Converted pixel size with the x 24 lens was 0.5micrometers . Magnification of the x-ray microscope system was set to be 7.61-13. Pitch of 0.6micrometers (0.3 micrometers line and 0.3micrometers space) pattern of the test chart was resolved, and the outermost zone structure of the same type of FZP was observed. Imaging properties are also discussed by using Hopkins optical imaging theory.