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Quantitative x-ray differential interference contrast microscopy
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|Title: ||Quantitative x-ray differential interference contrast microscopy|
|Authors: ||Nakamura, Takashi|
|Keywords: ||Biomedical engineering;X-ray microscopy;X-ray optics|
|Issue Date: ||11-Jul-2011|
|Abstract: ||Full- eld soft x-ray microscopes are widely used in many elds of sciences. Advances in nanofabrication technology enabled short wavelength focusing elements with signi cantly improved spatial resolution. In the soft x-ray spectral region, samples as small as 12 nm can be resolved using micro zone-plates as the objective lens. In addition to conventional x-ray microscopy in which x-ray absorption di erence provides the image contrast, phase contrast mechanisms such as di erential phase contrast (DIC) and Zernike phase contrast have also been demonstrated. These phase contrast imaging mechanisms are especially
attractive at the x-ray wavelengths where phase contrast of most materials is typically 10 times stronger than the absorption contrast. With recent progresses in plasma-based xray sources and increasing accessibility to synchrotron user facilities, x-ray microscopes are quickly becoming standard measurement equipment in the laboratory.
To further the usefulness of x-ray DIC microscopy, this thesis explicitly addresses three known issues with this imaging modality by introducing new techniques and devices. First, as opposed to its visible-light counterpart, no quantitative phase imaging technique exists for x-ray DIC microscopy. To address this issue, two nanoscale x-ray quantitative phase imaging techniques, using exclusive OR (XOR) patterns and zone-plate doublets, respectively, are proposed. Unlike existing x-ray quantitative phase imaging techniques such as Talbot interferometry and ptychography, no dedicated experimental setups or stringent illumination coherence are needed for quantitative phase retrieval.
Second, to the best of our knowledge, no quantitative performance characterization of DIC microscopy exists to date. Therefore, the imaging system's response to sample's spatial frequency is not known. In order to gain in-depth understanding of this imaging modality, performance of x-ray DIC microscopy is quanti ed using modulation transfer function. A new illumination apparatus required for the transfer function analysis under partially coherent illumination is also proposed. Such a characterization is essential for a proper selection of DIC optics for various transparent samples under study.
Finally, optical elements used for x-ray DIC microscopy are highly absorptive and high brilliance x-ray sources such as synchrotrons are generally needed for image contrast. To extend the use of x-ray DIC microscopy to a wider variety of applications, a high e ciency large numerical aperture optical element consisting of high re
ective Bragg re
ectors is proposed. Using Bragg re
ectors, which have 70% 99% re
ectivity at extreme ultraviolet and soft x-rays for all angles of glancing incidence, the rst order focusing e ciency is expected to increase by 8 times compared to that of a typical Fresnel zone-plate. This thesis contributes to current nanoscale x-ray phase contrast imaging research and provides new insights for biological, material, and magnetic sciences.|
|Appears in Collections:||Drexel Theses and Dissertations|
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