August 2007 Archives

The use of coherent X-rays makes it possible to replace lenses by signal processing in X-ray imaging techniques, as demonstrated for the first time in 1999 (See, J. Miao et al., Nature, 400, 342 (1999)). The current state-of-the-art technique uses radiation produced by a free-electron laser, which, in a single shot, images with a temporal resolution of 25 fs and a spatial resolution of 90 nm. Very recently, a group led by Professors H. Kapteyn and M. Murnane (University of Colorado, Boulder, USA) has succeeded in performing this kind of measurement in an ordinary laboratory, instead of at a synchrotron facility, using 29 nm soft X-rays generated as 25-31^th order harmonics from a 1.3 mJ, 25 fs, Ti:S laser. The team collected scattering from the sample by means of an X-ray CCD camera. The spatial resolution of the reconstructed images is 214 nm. For more information, see the paper, "Lensless Diffractive Imaging Using Tabletop Coherent High-Harmonic Soft-X-Ray Beams", R. L. Sandberg et al., Phys. Rev. Lett. 99, 098103 (2007)

Dr. H. Chapman (Lawrence Livermore National Laboratory, USA) and his colleagues recently published their new imaging technique, which is a new type of X-ray holography, and some successful data obtained at the free electron laser source, FLASH, Hamburg, Germany. Their technique employs soft X-ray laser pulses which pass through a small hole in a detector mirror, and then encounter a thin, translucent membrane that has been covered with a sample material (140 nm-diameter polystyrene balls) lying just in front of a backing mirror. In the present case, the X-ray pulse is shorter than the time spent traveling through the sample to the backing mirror and then returning. The sample is exploded by extremely strong X-ray photons and its size changes in the brief interval that the pulse takes to reflect back. The time it takes the pulse to return is encoded in the fringe pattern of the X-ray hologram, and this can be read out from the hologram to an accuracy of about one femtosecond. The spatial resolution is 50 nm in this experiment, but this will be further improved by shorter wavelength laser pulses. Their newly developed method opens up new opportunities for structure sciences based on holography, interferometry or coherent diffraction, as well as for studies that investigate the femtosecond dynamics of matter in new ways. It is interesting that the scientists were inspired by Isaac Newton, who noticed in the 18th century that sunlight produced "strange and surprising" light and dark bands on a screen after he had bounced it off a mirror speckled with dust particles. For more information, see the paper, "Femtosecond time-delay X-ray holography ", H. N. Chapman et al., Nature,. 448, 676-679 (2007).

The following awards were presented during the plenary session of the 56th Annual Denver X-Ray Conference:
1. The 2007 Barrett Award was presented to Sunil K. Sinha, University of California San Diego, La Jolla, CA
2. The 2007 Jenkins Award was presented to Ting C. Huang, Emeritus, IBM Almaden Research Center, San Jose, CA
3. The 2007 Distinguished Fellow Award was presented to Ting C. Huang, Emeritus, IBM Almaden Research Center, San Jose, CA
4. The 2007 Hanawalt Award was presented to Tamás Ungár, Eötvös University Budapest, Budapest, Hungary
5. There was no recipient for the 2007 Jerome B. Cohen Student Award.