Biomedical subjects

Jeffrey Bokor

Publications and source records attributed to Jeffrey Bokor.

3 recordsLinked to original sources

PubMed2003

Study of surface and bulk acoustic phonon excitations in superlattices using picosecond ultrasonics.

We have performed picosecond ultrasonic studies on the surface and bulk acoustic phonons in amorphous Mo/Si superlattices. Localized surface modes within the first, second, and sixth frequency gaps of the zone-folded phonons are observed. A selection rule derived from symmetry considerations provides new understanding of why certain modes are seen and not the others. The excitation strengths and detailed spectral features of these lines are studied, and the results are well explained by an elastic-continuum theory. It is found that the line shapes are significantly modified by the presence of bulk modes near the zone center.

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PubMed2003

Fourier-synthesis custom-coherence illuminator for extreme ultraviolet microfield lithography.

Scanning illumination systems provide for a powerful and flexible means for controlling illumination coherence properties. Here we present a scanning Fourier synthesis illuminator that enables microfield extreme ultraviolet lithography to be performed on an intrinsically coherent synchrotron undulator beamline. The effectiveness of the system is demonstrated through a variety of print experiments, including the use of resolution enhancing coherence functions that enable the printing of 50-nm line-space features by use of a lithographic optic with a numerical aperture of 0.1 and an operational wavelength of 13.4 nm.

Journal Article↗

PubMed2002

Fourier transform interferometer alignment method.

A rapid and convenient method has been developed to facilitate the alignment of the image-plane components of point-diffraction interferometers, including the phase-shifting point-diffraction interferometer. In real time, the Fourier transform of the detected image is used to calculate a pseudoimage of the electric field in the image plane of the test optic where thecritical alignment o f variousoptical components is performed. Reconstruction of the pseudoimage is similar to off-axis, Fourier transform holography. Intermediate steps in the alignment procedure are described. Fine alignment is aided by the introduction and optimization of a global-contrast parameter that is easily calculated from the Fourier transform. Additional applications include the alignment of image-plane apertures in general optical systems, the rapid identification of patterned image-plane alignment marks, and the probing of important image-plane field properties.

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