Scientists produce best hologram yet

August 2nd, 2008 - 3:07 pm ICT by IANS  

Washington, Aug 2 (IANS) Inspired by the pinhole camera technique, scientists have produced two of the brightest, sharpest x-ray holograms of microscopic objects, thousands of times more efficiently than previous x-ray-holographic methods. The x-ray hologram made at the Advanced Light Source (ALS) beamline 9.0.1 was of Leonardo da Vinci’s famous drawing, “Vitruvian Man”, a lithographic reproduction less than two millionths of a metre, or microns square, etched with an electron-beam nanowriter.

The other hologram, made at FLASH, was of a single bacterium, Spiroplasma milliferum, made at 150-nanometre resolution and computer-refined to 75 nanometres, but requiring an exposure to the beam of just 15 femtoseconds (quadrillionths of a second).

The values for these two holograms are among the best ever reported for micron-sized objects. With already established technologies, resolutions obtained by these methods could be pushed to only a few nanometres, or, using computer refinement, even better.

“Our purpose was to explore methods of making images of nanoscale objects on the time scale of atomic motions, a length and time regime that promises to become accessible with advances in free-electron lasers,” said Stefano Marchesini of the ALS, who led the research.

“The technique we used is called massively parallel x-ray Fourier-transform holography, with ‘coded apertures’. What inspired me to try this approach was the pinhole camera.”

The ancient Greeks made note of pinhole-camera effects without understanding them; later, pinhole cameras were used by Chinese, Arab, and European scholars. Renaissance painters learned the principals of perspective using the camera obscura, literally a “dark room”, with a pinhole in one wall that projected the outside scene onto the opposite wall.

“The room had to be dark for the good reason that a sharp image requires a small pinhole, but a small pinhole also produces a dim image,” says Marchesini. “To get a brighter image without lenses you have to use many pinholes. The problem then becomes how to assemble the information, including depth information, from the overlapping shadow images. This is where ‘coded apertures’ come in.”

By knowing the precise layout of a pinhole array, including the different sizes of the different pinholes, a computer can recover a bright, high-resolution image numerically.

Berkeley Lab, University of Hamburg and Dutsches Elektronen-Synchrotron (DESY), Germany, collaborated on the project.

Their results appear in advanced online publication of Nature Photonics.

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