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 〈Ms〉 = 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.
Highlights
X-ray free electron lasers (XFEL) operate on the principle of self amplified spontaneous emission (SASE)
We demonstrate that a single shot speckle visibility analysis offers a versatile and suitable ways of measuring coherence of the hard x-ray Free-electron lasers (FELs) pulses
In the small angle x-ray scattering (SAXS) configuration, our single shot result shows that the focused FEL beam is transversely coherent with marginal pulse-topulse variation
Summary
X-ray free electron lasers (XFEL) operate on the principle of self amplified spontaneous emission (SASE). They can deliver orders of magnitude more brilliant coherent radiation than previously available from synchrotron storage ring sources, tunable from VUV to the hard xray regime [1,2,3,4,5]. Due to the amplification process, which starts from the electron beam shot noise, the FEL carries different operational parameters as compared to storage ring based 3rd generation light sources. A comprehensive analysis of the FEL single shot coherence properties is of fundamental interest and is a necessity to take full benefit of these new light sources
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