Generating X-rays that have the properties of laser light has been a long-standing goal for experimental science. Here we describe the emission of highly collimated, spatially coherent X-rays, at a wavelength of about 1 nanometre and at photon energies extending to 1.3 kiloelectronvolts, from atoms that have been ionized by a 5-femtosecond laser pulse. This means that a laboratory source of laser-like, kiloelectronvolt X-rays, which will operate on timescales relevant to many chemical, biological and materials problems, is now within reach.

Trace elements are chemical elements in minute quantities, which are known to accumulate in the bone. Cortical and trabecular bones consist of bone structural units (BSUs) such as osteons and bone packets of different mineral content and are separated by cement lines. Previous studies investigating trace elements in bone lacked resolution and therefore very little is known about the local concentration of zinc (Zn), strontium (Sr) and lead (Pb) in BSUs of human bone. We used synchrotron radiation induced micro X-ray fluorescence analysis (SR μ-XRF) in combination with quantitative backscattered electron imaging (qBEI) to determine the distribution and accumulation of Zn, Sr, and Pb in human bone tissue.Fourteen human bone samples (10 femoral necks and 4 femoral heads) from individuals with osteoporotic femoral neck fractures as well as from healthy individuals were analyzed. Fluorescence intensity maps were matched with BE images and correlated with calcium (Ca) content. We found that Zn and Pb had significantly increased levels in the cement lines of all samples compared to the surrounding mineralized bone matrix. Pb and Sr levels were found to be correlated with the degree of mineralization. Interestingly, Zn intensities had no correlation with Ca levels. We have shown for the first time that there is a differential accumulation of the trace elements Zn, Pb and Sr in BSUs of human bone indicating different mechanisms of accumulation.

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Strontium ranelate (SrR) is a relatively new treatment for osteoporosis. In this study we investigated its potential impact on human bone material quality in transiliac bone biopsies from postmenopausal osteoporotic women treated 3 years with calcium and vitamin D plus either 2 g SrR per day or placebo. Bone mineralization density distribution (BMDD), strontium (Sr) concentration, collagen cross-link ratio, and indentation modulus were analyzed by quantitative backscattered electron imaging, electron-induced X-ray fluorescence analysis, synchrotron radiation induced micro X-ray fluorescence elemental mapping, Fourier transform infrared imaging, and nanoindentation, respectively. The BMDD of SrR-treated patients was shifted to higher atomic numbers (Z mean þ1.5%, p < .05 versus placebo). We observed Sr being preferentially incorporated in bone packets formed during SrR treatment up to 6% atom fraction [Sr/(Sr þ Ca)] depending on the SrR serum levels of the individuals (correlation r ¼ 0.84, p ¼ .018). Collagen cross-link ratio was preserved in SR-treated bone. The indentation modulus was significantly decreased in younger versus older bone packets for both placebo-(À20.5%, p < .0001) and SrR-treated individuals (À24.3%, p < .001), whereas no differences were found between the treatment groups. In conclusion, our findings indicate that after SrR treatment, Sr is heterogeneously distributed in bone and preferentially present in bone packets formed during treatment. The effect of SrR on BMDD seems to be due mainly to the uptake of Sr and not to changes in bone calcium content. Taken together, these data provide evidence that the investigated bone quality determinants at tissue level were preserved in postmenopausal osteoporotic women after 3-year treatment with 2 g SrR per day plus calcium and vitamin D. ß

Helium atoms ionized by intense few-cycle light pulses in the barrier suppression regime emit spatially coherent extreme ultraviolet continuum extending to photon energies greater than E ph 0.5 keV (l , 2.5 nm). The high-energy end of the continuum in the range of E ph $ 0.2 keV (l # 6 nm) was characterized spectrally over a considerable dynamic range using energy-dispersive detection. The sub-10-fs laser pulse duration was found to be crucial for generating radiation with the highest photon energies at the low (,0.5 mJ) pump energy levels used in the experiments. The single-atom quantum theory of high-order harmonic generation combined with Maxwell's wave equation provides a satisfactory account for the experimental observations. [S0031-9007(98)05814-1] PACS numbers: 42.65. Ky, 41.50. + h, 42.50.Hz, 42.65.Re This Letter reports the generation of coherent x rays with photon energies in excess of 500 eV (corresponding to wavelengths shorter than 2.5 nm) in a helium gas jet irradiated by near-infrared sub-mJ, sub-10-fs optical pulses at a 1-kHz repetition rate. This radiation constitutes the shortest-wavelength coherent light reported to date. The x rays are emitted in a well-collimated beam with a divergence that decreases with increasing photon energy. The 1-kHz repetition rate of the laser driver allowed the use of highly sensitive energy-dispersive x-ray spectrometry (EDS), which permitted high-dynamic-range (ഠ10 3 ) spectral characterization of a high-harmonic source in the sub-keV range for the first time. These measurements provide insight into a new regime of extreme ultraviolet (XUV) high-harmonic (or continuum) generation in which the atoms undergo ionization with their Coulomb barrier suppressed below the ground-state energy level during the interaction responsible for high-energy XUV emission. Comparison of the observed spectra with results of theoretical simulations points to the key role of dephasing during propagation.Coherent harmonic emission from atomic ensembles exposed to ultrashort laser pulses has been previously observed up to photon energies many times higher than the potential energy of bound electrons in the atomic Coulomb field [1-3]. In a semiclassical picture, this phenomenon has been understood in terms of tunnel ionization of the atom, followed by acceleration of the electron in the external field and recombination with its parent ion [4,5]. These processes take place over an optical period and are repeated quasiperiodically in laser pulses that comprise many oscillation cycles, leading to the emission of high harmonics of the driving field. The highest harmonic photon energy is given by ͑E ph ͒ max ഠ I p 1 3.2U p , where I p is the ionization potential of the atom, and U p is the ponderomotive potential of the laser field [3][4][5]. Here U p in eV is approximately given by 0.93 3 10 213 I s l 2 , where l is the carrier wavelength in mm and I s is the saturation intensity in W͞cm 2 , which the atoms can be exposed to before the ground state is depleted; i.e., the ensemble is fully ...