PORTLAND, Ore. An international team of researchers combined an X-ray laser and a lens-less pinhole camera to demonstrate the world's smallest and highest-resolution holograms of micron-size objects at nanometer resolution.
By placing the camera's aperture very close to the object and using an array of hundreds of different-size pinholes, a computer was able to reconstruct the holograms, according to researchers in the United States, Germany and Sweden.
The team displayed two images--a 3-D rendering of a single bacterium and a lithographic reproduction of Leonardo da Vinci's "Vitruvian Man"--to demonstrate the feasibility of nanometer-resolution holographic X-ray images of micron-size objects. The project showed that holographic X-ray images with femtosecond exposure times can freeze the action of atomic-scale operations--such as chemical actions--to advance nanotechnology, the team said.
|Coherent X-rays illuminate both the object and a uniformly redundant array of pinholes, while the CCD detector images diffracted X-rays from both to produce a hologram from the resultant interference pattern. Photo courtesy of Lawrence Berkeley National Laboratory|
The team used the Advanced Light Source (ALS) at the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the Free Electron Laser, known as Flash, in Hamburg, Germany. Other scientists involved in the project reside at the Stanford Linear Accelerator Center (California), Uppsala University (Sweden), the University of Hamburg, the Deutsches Elektronen-Synchrotron (DESY, Germany), Arizona State University (Tempe), Princeton University (New Jersey) and the University of California at Berkeley.
Pinhole cameras act as a single point through which all light beams emanating from an object must pass. The beams come straight from an object, through the pinhole, then onto a photographic plate (here, a charge-coupled device, or CCD). The image is inverted, since beams coming from the top of the object and passing through the single point end up at the bottom of the imager. Likewise, beams from the bottom pass through the pinhole and end up at the top of the imager.
Meanwhile, holography works by using two beams of coherent lasers to record an image--one to illuminate the object and a second reference beam. The result is an interference pattern that gets recorded by the imager and reproduced on a transparency. Then, by illuminating it with the reference beam alone, the original 3-D image is reconstructed on the focal plane behind the transparency.
Stefano Marchesini, a scientist at Lawrence Berkeley National Laboratory, conceived the idea of combining these two techniques using an approach already proven for constructing gamma-ray images of astronomical objects: Fourier-transform holography with coded apertures in a uniformly redundant array. By using hundreds of variously sized pinholes and computer algorithms, the team was able to reconstruct the resultant images captured by the CCD.
Because the objects to be imaged were micron-sized, the team needed an extremely bright source of light at X-ray wavelengths, which they found at ALS in the United States and at Flash in Germany. Illuminating the micron-size objects with these X-ray sources produced the world's highest-resolution holograms.
ALS imaged Leonardo da Vinci's "Vitruvian Man," which had previously been etched with an electron-beam "nanowriter," into a 2-micron-wide lithographic reproduction. The team used a 5-second exposure to achieve a resolution of 50 nm.
Flash imaged a single, micron-size Spiroplasma milliferum bacterium to achieve a computer-enhanced resolution of 75 nm with an ultrashort exposure time of 15 femtoseconds.
Next, the researchers plan to push the limit of their technique to achieve computer-enhanced resolutions of just a few nanometers. The ultrafast, femtosecond exposure times are capable of freezing the action of never-before-seen operations, such as the atomic motion of nanoscale chemical reactions.