We studied experimentally and theoretically the structural transition of diamond under an irradiation with an intense femtosecond extreme ultraviolet laser (XUV) pulse of 24-275 eV photon energy provided by free-electron lasers. Experimental results obtained show that the irradiated diamond undergoes a solid-to-solid phase transition to graphite, and not to an amorphous state. Our theoretical findings suggest that the nature of this transition is nonthermal, stimulated by a change of the interatomic potential triggered by the excitation of valence electrons. Ultrashort laser pulse duration enables to identify the subsequent steps of this process: electron excitation, band gap collapse, and the following atomic motion. A good agreement between the experimentally measured and theoretically calculated damage thresholds for the XUV range supports our conclusions. It is often observed that a femtosecond irradiation of a material induces an atomic disorder therein: amorphization, or defect creation. Graphitization of diamond is a counterexample as it is an order-to-order (solid-to-solid) phase transition. It illustrates the fundamental interplay between the bonding, respectively sp 3 and sp 2 bonds for diamond and graphite, and the structure, respectively cubic and hexagonal. The advent of extreme ultraviolet (XUV) and x-ray free-electron lasers (XFELs), delivering femtosecond intense pulses in the soft to hard x-ray domain allows investigating the structural transition of diamond within this unexplored regime and clarifying whether it leads to an ordered or disordered state. In our study we show the experimental results of the XUV irradiation of diamond followed by a dedicated theoretical analysis.Irradiation by an optical femtosecond laser pulse triggers a specific process known as a nonthermal phase transition, which has been demonstrated for a class of materials.1 However, there are still active debates over the nature of the observed nonthermal transitions, e.g., see Ref. 2. For this type of transition, models predict that the excitation of a few percent of the valence band electrons leads to a drastic modification of the potential energy surface, triggering the displacement of the atoms. This process occurs on a much faster time scale (subpicosecond) than the transfer of the absorbed laser energy to the lattice via electron-phonon coupling. Such a nonthermal phase transition still needs to be observed in the x-ray regime.In the XUV and x-ray domain the excitation of electrons is only due to single photon absorption, and the absorption by free electrons does not occur. As a result, the first stage of the interaction, electron excitation and heating, which are driving nonthermal processes, is quite different compared to the optical regime.1 It is then questionable if a nonthermal phase transition can be triggered by an XFEL pulse. In the present Rapid Communication we identify the phase transition, which diamond undergoes under femtosecond XUV irradiation, as the graphitization. We show that the final state of the...

X-ray fluorescence techniques have proven beneficial for identifying and quantifying trace elements in biological tissues. A novel approach is being developed that employs x-ray fluorescence with an aim to locate heavy nanoparticles, such as gold, which are embedded into tissues. Such nanoparticles can be functionalized to act as markers for tumour characteristics to map the disease state, with the future aim of imaging them to inform cancer therapy regimes. The uptake of functionalized nanoparticles by cancer cells will also enable detection of small clusters of infiltrating cancer cells which are currently missed by commonly used imaging modalities. The novel system, consisting of an energy-resolving silicon drift detector with high spectral resolution, shows potential in both quantification of and sensitivity to nanoparticle concentrations typically found in tumours. A series of synchrotron measurements are presented; a linear relationship between fluorescence intensity and gold nanoparticle (GNP) concentration was found down to 0.005 mgAu ml(-1), the detection limit of the system. Successful use of a bench-top source, suitable for possible future clinical use, is also demonstrated, and found not to degrade the detection limit or accuracy of the GNP concentration measurement. The achieved system sensitivity suggests possible future clinical usefulness in measuring tumour uptake in vivo, particularly in shallow tumour sites and small animals, in ex vivo tissue and in 3D in vitro research samples.

X-ray Free Electron Lasers (XFELs) have the potential to contribute to many fields of science and to enable many new avenues of research, in large part due to their orders of magnitude higher peak brilliance than existing and future synchrotrons. To best exploit this peak brilliance, these XFEL beams need to be focused to appropriate spot sizes. However, the survivability of X-ray optical components in these intense, femtosecond radiation conditions is not guaranteed. As mirror optics are routinely used at XFEL facilities, a physical understanding of the interaction between intense X-ray pulses and grazing incidence X-ray optics is desirable. We conducted single shot damage threshold fluence measurements on grazing incidence X-ray optics, with coatings of ruthenium and boron carbide, at the SPring-8 Angstrom compact free electron laser facility using 7 and 12 keV photon energies. The damage threshold dose limits were found to be orders of magnitude higher than would naively be expected. The incorporation of energy transport and dissipation via keV level energetic photoelectrons accounts for the observed damage threshold.

The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called “molecular movie” within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.

The interaction of free electron laser pulses with grating structure is investigated using 4.6 0.1 nm radiation at the FLASH facility in Hamburg. For fluences above 63.7 8.7 mJ∕ cm 2 , the interaction triggers a damage process starting at the edge of the grating structure as evidenced by optical and atomic force microscopy. Simulations based on solution of the Helmholtz equation demonstrate an enhancement of the electric field intensity distribution at the edge of the grating structure. A procedure is finally deduced to evaluate damage threshold.