Single Shot Spatial and Temporal Coherence Properties of the SLAC Linac Coherent Light Source in the Hard X-Ray Regime

Abstract

We measured the transverse and longitudinal coherence properties of the Linac Coherent Light Source (LCLS) at SLAC in the hard x-ray regime at 9 keV photon energy on a single shot basis. Speckle patterns recorded in the forward direction from colloidal nanoparticles yielded the transverse coherence properties of the focused LCLS beam. Speckle patterns from a gold nanopowder recorded with atomic resolution allowed us to measure the shot-to-shot variations of the spectral properties of the x-ray beam. The focused beam is in the transverse direction fully coherent with a mode number close to 1. The average number of longitudinal modes behind the Si(111) monochromator is about 14.5 and the average coherence time τ(c)=(2.0±1.0) fc. The data suggest a mean x-ray pulse duration of (29±14) fs behind the monochromator for (100±14) fc electron pulses.

Single-shot pulse duration monitor for extreme ultraviolet and X-ray free-electron lasers

“…The electron bunch durations at 5.5 nm are considerably shorter than 100 fs, but corresponding measurements are not published yet. The correlation between bunch charge and FEL pulse duration is derived from techniques developed earlier, for example, XUV autocorrelation 24,25 , XUV/ optical cross-correlation 26 , spectral measurements and statistical methods [27][28][29][30][31][32] , and terahertz streaking 22,23 . These complex techniques are not available on demand for direct comparison.…”

“…Direct and indirect techniques for XUV and X-ray pulse duration measurement [22][23][24][25][26][27][28][29][30][31][32] and pulse arrival time monitoring [11][12][13][14][15][16][17][18][19][20][21][22][23] are subjects of active research and most are already implemented in the FEL machine environment. In particular for XUV pulses, the experiments must be realized under vacuum conditions.…”

Two-dimensional stimulated resonance Raman spectroscopy of molecules with broadband x-ray pulses

“…23,24 The source is intense enough to create hollow atoms by depopulating both core orbitals for a resonant transition within the Auger decay time of the core-hole in atomic 25 and molecular 26 systems. One drawback of XFEL radiation is that the coherence time is short (<5 fs), 27 a consequence of quantum statistics in the electron bunch used to generate the pulse. Despite this drawback, the high intensity of the LCLS XFEL source make it the most likely candidate for exciting nonlinear x-ray transitions.…”

Ultrafast population transfer to excited valence levels of a molecule driven by x-ray pulses

“…This mechanism permits site specificity; the initial valence excitation is localized on the atomic center supporting the core excitation, and its subsequent evolution across the molecule may be probed by core transitions on other centers. The scientific motivations for the proposed construction of new free-electron laser facilities [4][5][6] generally include this class of experiments as a principal goal.…”