Generation Of X-ray Free-electron Lasers Research Articles

Use of diamond sensors for a high-flux, high-rate X-ray pass-through diagnostic.

X-ray free-electron lasers (XFELs) deliver pulses of coherent X-rays on the femtosecond time scale, with potentially high repetition rates. While XFELs provide high peak intensities, both the intensity and the centroid of the beam fluctuate strongly on a pulse-to-pulse basis, motivating high-rate beam diagnostics that operate over a large dynamic range. The fast drift velocity, low X-ray absorption and high radiation tolerance properties of chemical vapour deposition diamonds make these crystals a promising candidate material for developing a fast (multi-GHz) pass-through diagnostic for the next generation of XFELs. A new approach to the design of a diamond sensor signal path is presented, along with associated characterization studies performed in the XPP endstation of the LINAC Coherent Light Source (LCLS) at SLAC. Qualitative charge collection profiles (collected charge versus time) are presented and compared with those from a commercially available detector. Quantitative results on the charge collection efficiency and signal collection times are presented over a range of approximately four orders of magnitude in the generated electron-hole plasma density.

Frequency-Mixing Lasing Mode at European XFEL

We demonstrate generation of X-ray Free-Electron Laser (XFEL) pulses in frequency mixing mode at the SASE3 line of the European XFEL. The majority of the SASE3 FEL segments are tuned at two frequencies ω1 and ω2 following an alternate pattern. Leveraging on non-linearities generated through longitudinal dispersion in the system, we obtain electron bunching at a frequency difference ωFM=ω2−ω1. FEL amplification at ωFM follows in a few last radiator segments. We report on the generation of frequency mixing at photon energies between 500 eV and 1100 eV with pulse energies, depending on the length of the radiator, in the mJ level. This method allows generating low photon energies in cases where the FEL runs at high electron energy and the target photon energy cannot be reached in the main undulator, with the simple addition of a short, custom-made afterburner.

X-ray free-electron lasers light up materials science

X-ray free-electron lasers (XFELs) are revolutionizing our ability to measure and understand the behaviour of complex materials. A new generation of XFELs is imminent, offering new approaches to materials characterization.

Reconstruction of diffraction patterns by using the Helmholz–Kirchhoff integral theorem

A new method to obtain three-dimensional information on atomic arrangement from a monochromatic Laue pattern based on the Helmholz–Kirchhoff integral theorem is presented and experimentally proved by applying the algorithm to the thermal diffuse scattering from a single crystal. The advantage given by the possibility of collecting all the required data on a position-sensitive detector in one shot opens new perspectives for studies of fast physical or chemical processes in three dimensions. The reduced exposure time can also avoid radiation damage of organic specimens, and, in conjunction with an ultra-bright beam from the next generation of X-ray free-electron lasers, makes the method suitable for structural studies with individual atomic clusters. This approach can also be used, by observing the thermal diffuse scattering or order diffuse scattering from both non-crystalline samples and `imperfect' crystals, for the investigation of short-range ordered arrangements of atoms.