High-Speed X-ray Imaging

August 5, 2009

Scientists from the European Synchrotron Radiation Facility (France) the Forschungszentrum Karlsruhe, the Technische Universität Berlin and the Helmholtz Zentrum Berlin (all Germany) were able to make fast processes inside opaque objects visible, by using white synchrotron radiation to perform hard X-ray radioscopy with high spatio-temporal resolution. The required imaging detector was constructed out of a standard indirect detector in combination with a Photron SA1 CMOS-based camera. Thus, it was possible to investigate pore coalescence and individual cell wall collapse in an expanding liquid metal foam: the rupture of a film and the subsequent merger of two neighbouring bubbles could be recorded with a time sampling rate of 40000 frames per second (25 micorseconds exposure time). The results as published in the Journal of Synchrotron Radiation (http://journals.iucr.org/s/issues/2009/03/00/kv5057/ – open access) allowed to determine that the pore stability in a liquid metal foam is driven by intertia and not the viscosity of the melt. This knowledge is crucial in order to adapt metal foaming process for industrial production.

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3D Movies of Microscopic Systems

Juli 29, 2009

Physicists at New York University (NYU), US have developed a technique to record three-dimensional movies of microscopic systems, such as biological molecules, through holographic video. The technique, developed in the laboratory of NYU Physics Professor David Grier, is comprised of two components: making and recording the images of microscopic systems and then analyzing these images. To generate and record images, the researchers created a holographic microscope. It is based on a conventional light microscope, which uses a collimated laser beam instead of on an incandescent illuminator.
When an object is placed into path of the microscope’s beam, the object scatters some of the beam’s light into a complex diffraction pattern. The scattered light overlaps with the original beam to create an interference pattern reminiscent of overlapping ripples in a pool of water. The microscope then magnifies the resulting pattern of light and dark and records it with a conventional digital video recorder. Each snapshot in the resulting video stream is a hologram of the original object. Unlike a conventional photograph, each holographic snapshot stores information about the three-dimensional structure and composition of the object that created the scattered light field. The recorded holograms appear as a pattern of concentric light and dark rings.
For analyzing the images the researchers based their work on a quantitative theory, the Lorenz-Mie theory, which maintains that the way light is scattered can reveal the size and composition of the object that is scattering it.
The application of the technique ranges from research in fundamental statistical physics to analyzing the composition of fat droplets in milk.

In the microscope, a laser beam illuminates the sample. Light scattered by the sample creates an interference pattern which is magnified and recorded. Then measurements of the particle’s position, size, and refractive index are obtained.

In the microscope, a laser beam illuminates the sample. Light scattered by the sample creates an interference pattern which is magnified and recorded. Then measurements of the particle’s position, size, and refractive index are obtained.

New Cloaking Technology

Mai 26, 2009

Researchers of Purdue University, West Lafayette, IN, US announced that they have created a new type of invisibility cloak which works for all colors of the visible spectrum. This new technology, based on a tapered optical waveguide, is simpler than previous designs and makes it possible to cloak objects of about 50 microns in diameter – roughly the width of a human hair. „All previous attempts at optical cloaking have involved very complicated nanofabrication of metamaterials containing many elements, which makes it very difficult to cloak large objects,“ said Vladimir Shalaev, Purdue University’s Robert and Anne Burnett Professor of Electrical Engineering. „Here, we showed that if a waveguide is tapered properly it acts like a sophisticated nanostructured material.” Previous experiments with metamaterials have been limited to cloaking regions only a few times larger than the wavelengths of visible light. This findings could lead to advances in e.g. cloaking; powerful “hyperlenses” resulting in microscopes 10 times more powerful than today’s; computers and consumer electronics that use light instead of electronic signals to process information; advanced sensors; and more efficient solar collectors. Findings are detailed in a research paper appearing May, 29 in Physical Review Letters.