Biomedical subjects

Chang Chang

Publications and source records attributed to Chang Chang.

4 recordsLinked to original sources

PubMed2006

Single-element objective lens for soft x-ray differential interference contrast microscopy.

High-resolution soft x-ray differential interference contrast (DIC) imaging was demonstrated through the use of a single-element objective, the XOR pattern, in a full-field soft x-ray microscope. DIC images of the magnetic domains in a 59 nm thick amorphous Gd25Fe75 layer were obtained and magnetic phase contributions were directly imaged. With its elemental, chemical, and magnetic specificity, compatibility with various sample environments, and ease of implementation, we expect this soft x-ray DIC technique to become one of the standard modes of operation for existing full-field soft x-ray microscopes.

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PubMed2006

Direct index of refraction measurements at extreme-ultraviolet and soft-x-ray wavelengths.

Coherent radiation from undulator beamlines has been used to directly measure the real and imaginary parts of the index of refraction of several materials at both extreme-ultraviolet and soft-x-ray wavelengths. Using the XOR interferometer, we measure the refractive indices of silicon and ruthenium, essential materials for extreme-ultraviolet lithography. Both materials are tested at wavelength (13.4 nm) and across silicon's L2 (99.8 eV) and L3 (99.2 eV) absorption edges. We further extend this direct phase measurement method into the soft-x-ray region, where measurements of chromium and vanadium are performed around their L3 absorption edges at 574.1 and 512.1 eV, respectively. These are the first direct measurements, to our knowledge, of the real part of the index of refraction made in the soft-x-ray region.

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PubMed2003

Analysis of illumination coherence properties in small-source systems such as synchrotrons.

Modern synchrotron beamlines often take the form of critical illumination systems, where an incohrent source of limited spatial extent is re-imaged to an experimental plane of interest. Unique constraints of synchrotron sources and beamline, however, may preclude the use of the simple Zernike approximation for calculating the object-image coherence relationship. Here, we perform a rigorous analysis of the object-image coherence relationship valid for synhrotron beamlines. The analysis shows that beamline aberrations have an effect on the coherence properties. Effects of various low-order aberrations on the coherence properties are explicitly studied.

Journal Article↗

PubMed2002

Diffractive optical elements based on Fourier optical techniques: a new class of optics for extreme ultraviolet and soft x-ray wavelengths.

A diffractive optical element, based on Fourier optics techniques, for use in extreme ultraviolet/soft x-ray experiments has been fabricated and demonstrated. This diffractive optical element, when illuminated by a uniform plane wave, will produce two symmetric off-axis first-order foci suitable for interferometric experiments. The efficiency of this optical element and its use in direct interferometric determination of optical constants are also discussed. Its use in direct interferometric determination of optical constants is also referenced. Its use opens a new era in the use of sophisticated optical techniques at short wavelengths.

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