Single shot speckle and coherence analysis of the hard X-ray free electron laser LCLS

Abstract

Abstract:The single shot based coherence properties of hard x-ray pulses from the Linac Coherent Light Source (LCLS) were measured by analyzing coherent diffraction patterns from nano-particles and gold nanopowder. The intensity histogram of the small angle x-ray scattering ring from nano-particles reveals the fully transversely coherent nature of the LCLS beam with a number of transverse mode M s = 1.1. On the other hand, the speckle contrasts measured at a large wavevector yields information about the longitudinal coherence of the LCLS radiation after a silicon (111) monochromator. The quantitative agreement between our data and the simulation confirms a mean coherence time of 2.2 fs and a x-ray pulse duration of 29 fs. Finally the observed reduction of the speckle contrast generated by x-rays with pulse duration longer than 30 fs indicates ultrafast dynamics taking place at an atomic length scale prior to the permanent sample damage. References and links1. M. Hogan, C. Peelegrini, J. Rosenzweig, S. Frigola, A. Tremaine, C. Fortgang, D. Nguyen, R. Sheffield, J. Kinross-Wright, A. Varfolomeev, A. Varfolomeev, S. Tolmachev, and R. Carr, "Measurement of gain larger than 10 5 at 12µm in a self-amplified spontaneous-emission free-electron laser," Phys. Rev. Lett. 81, 4867-4870 (1998

Single Shot Coherence Properties of the Free-Electron Laser SACLA in the Hard X-ray Regime

“…In particular, every single X-ray shot is expected to show certain random features because of the stochastic nature of the SASE process. This was observed recently in experiments at the LCLS and in simulations on the longitudinal coherence properties, where a significant shot-to-shot variation has been observed13. In contrast, a SASE beam is expected to show a superior transverse coherence12.…”

The X-ray Correlation Spectroscopy instrument at the Linac Coherent Light Source

“…a measure of the transverse coherence in the small-angle regime Hruszkewycz et al, 2012;Lee et al, 2013;Lehmkü hler et al, 2014). The intensities from a narrow iso-Q area consisting of an annulus centered at Q = 0 with a radius Q are histogrammed as displayed in Fig.…”

Small-Angle X-Ray Scattering of Ionic Liquids

“…6.14 [123]. The left panel shows a single coherent scattering speckle pattern, and the right panel shows the incoherent summation from 50 consecutive measurements, which, as discussed above, is analogous to data from a conventional incoherent SAXS measurement.…”