October 2010 Archives

When an X-ray source with extremely high brilliance such as an X-ray free electron laser is used for X-ray spectroscopy experiments, we have to consider the significant population of the two core-hole states because of two-photon x-ray absorption (see, for example, the previous news article, ""Hollow" neon atom created by X-ray laser excitation" in X-ray Spectrometry, Vol. 39, No.5 (2010)). A research group led by Professor F. Gel'mukhanov (Royal Institute of Technology, Sweden) has recently published the calculation of the resonant X-ray emission from a neon atom induced by the two-photon population of a double-core-hole excited state. They studied mainly 2 cases; an off-resonant intermediate single-core-hole state, and a resonant core-ionized intermediate state. For more information, see the paper, "Two-photon-induced x-ray emission in neon atoms", Y-P. Sun et al., Phys. Rev. A 82, 043430 (2010).

A number of new methods have been proposed of late to produce X-ray photons with high brightness and short pulse duration, namely extremely high order harmonics from a laser, inverse Compton scattering and laser plasma acceleration. Dr. S. Kneip and his colleagues have recently applied the last of these types of technology to a table top synchrotron X-ray source. The method uses the phenomenon whereby the passage of an intense laser pulse through an underdense plasma generates a so-called plasma wakefield, which can have intrinsic fields of 1,000 times or more the best achievable by conventional accelerator technology. Some readers might recall previous news articles, "Table-top soft X-ray undulator source" in X-ray Spectrometry, Vol. 39, No.1 (2010) and "A compact synchrotron light source driven by pulse laser", in X-ray Spectrometry, Vol. 37, No.2 (2008). Both are pioneering reports on wakefield-driven synchrotron radiation. After generating high-energy electrons by laser pulse, they tried to transport the beam to an undulator, which is a magnet array and usually known as an insertion device placed at the straight section of the storage ring. In contrast, the electron beam in the plasma accelerator undergoes transverse (betatron) oscillations when subject to the focusing fields of the plasma wave, and the radiation wavelength can extend to the hard X-ray region as well. The research group succeeded in enhancing the brilliance of this betatron radiation by optimizing the wakefield conditions. They were able to accelerate electrons upto 230 MeV with a 5 mm path, and the critical energy of the obtained radiation was 6-10 keV. For more information, see the paper, "Bright spatially coherent synchrotron X-rays from a table-top source", S. Kneip et al., Nature Physics, (2010) (Published online, DOI:10.1038/nphys1789).

The recipient of the 5th Asada Award, which is presented by the Discussion Group of X-ray Analysis, Japan, in memory of the late Professor Ei-ichi Asada (1924-2005) to promising young scientists in X-ray analysis fields in Japan, is Dr. Tsutomu Kurisaki (Fukuoka Univ., "Development of a novel soft X-ray absorption spectroscopic measurement apparatus and structural analysis of various metals ions and metal complexes in aqueous solution"). The ceremony was held during the 46th Annual Conference on X-Ray Chemical Analysis, Japan, at the Hiroshima Prefectural Information Plaza, Hiroshima.

Dr. I. Han (Ağrι İbrahim Çeçen University, Turkey) and his colleagues have published a paper on the relationship between the Kβ/Kα X-ray fluorescence intensity ratio and valence-electron configurations in Ti_xCo_1-x (x = 0.7, 0.6, 0.5, 0.4, and 0.3). For more information, see the paper, "Relative K x-ray intensity studies on valence-electron structure of Ti and Co in Ti_xCo_1-x alloys", I. Han et al., Phys. Rev. A82, 042514 (2010).

A research group led by Professor H. Zabel (Ruhr-Universität Bochum, Germany) has recently published an interesting paper discussing the solution to a well-known problem in X-ray reflectivity. The technique is for layered thin films, and can give the layer thickness, surface/interface roughness and correlations of the interface roughness parallel and perpendicular to the interface. Due to the finite size of the receiving detector slit, it will always collect not only pure specular reflection but also diffusely scattered radiation. For many years, the separation of the diffuse contribution to the intensity of specular reflection has been an important topic for reliable data analysis. The researchers propose several measurements using different slit openings for specular scans, and show some applications to realistic systems, such as periodic V/Fe multilayers prepared on MgO substrate, with V and Pd capping layers. For more information, see the paper, "Separation of the diffuse contribution to the specular x-ray scattering of multilayer films", V. P. Romanov et al., Phys. Rev. B 82, 165416 (2010).