A collaboration of American and European scientists is working on an X-ray holographic technique, which promises the ability to image individual molecules within a living cell
From Lawrence Livermore National Lab:
For now, the Advanced Light Source at LBNL and the FLASH facility in Hamburg, Germany, are being used to provide the X-ray beams. But a new facility under construction at Stanford University, the Linac Coherent Light Source (LCLS), will provide additional capabilities and greater imaging accuracy when it comes on line next year.
Another light source being built in Hamburg will be used as well. When completed in late 2013, the X-ray Free Electron Laser (XFEL) will be the world’s longest artificial light source.
Using high-energy, extremely short-pulse — less than 100 femtoseconds, or one quadrillionth of a second — X-ray beams to examine nanoscale objects is not a new concept. The difficulty lies with the algorithms to convert the resulting patterns into usable images.
One method to increase the signal and resolution of the image is to include a second item with known features during the laser imaging. Known as a “reference object,” it gives the researchers additional information with which to process the imaging data.
What is new is to use a very special reference object called a “uniformly redundant array” (URA). In this case, a combination of complex formulas known as a “Fourier Transform” and a “Hadamard Transform” are utilized to convert the data into an image that represents the object being examined. Hadamard transforms are commonly used in signal processing and data algorithms, including those used in photo and video compression.
According to Hau-Riege, “The resolution we achieved is among the best ever reported for holography of a micrometer-sized object, and we believe that it will improve in the future with the development of nano-arrays for Fourier Transform Holography at LCLS.”
Press release: Improving our ability to peek inside molecules
Image: a) A lithographic test sample imaged by scanning electron microscopy (SEM) next to a 30-nm-thick twin-prime 71 x 73 array with 44-nm square gold scattering elements. The scale bar is 2 mm. b) The diffraction pattern collected at the ALS (1 x 10 6 photons in a five second exposure, 200 mm from the sample). c) The real part of the reconstructed hologram. d) The simulation with 1 x 10 6 photons. The grey scale represents the real part of the hologram. e) A simulation with the same number of photons, but a single reference pinhole. f) Line through the two dots indicated in image c.
