Single pulse coherence measurements in the water window at the free-electron laser FLASH

Abstract

The spatial coherence of free-electron laser radiation in the water window spectral range was studied, using the third harmonic (λ<(3rd) = 2.66 nm) of DESY's Free-electron LASer in Hamburg (FLASH). Coherent single pulse diffraction patterns of 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) multilamellar lipid stacks have been recorded. The intensity histogram of the speckle pattern around the first lamellar Bragg peak, corresponding to the d = 5 nm periodicity of the stack, reveals an average number of transverse modes of M¯ = 3.0 of the 3rd harmonic. Using the lipid stack as a 'monochromator', pulse-to-pulse fluctuations in the third harmonic λ(3rd) have been determined to be 0.033 nm.

Radiation characteristics of extreme UV and soft X-ray sources

“…Existing coherence studies pose simplifying assumptions on the FEL beam [23,24,25], e.g., that it can be described by the Gaussian Schell-model. Here, the four-dimensional mutual coherence function (MCF) is determined for the photon beam of FLASH without theoretical restrictions.…”

“…The spatial coherence properties of free-electron lasers are addressed in many publications employing Young's double pinhole experiment [23], speckle statistics [24] or Hanbury Brown-Twiss interferometry [25]. However, in these studies a comprehensive characterization of the four-dimensional mutual coherence function is only possible if the FEL beam follows the Gaussian Schell-model.…”

X-Ray Near-Field Holography: Beyond Idealized Assumptions of the Probe

“…Wavefront sensing and coherence measurements have therefore attracted significant attention in the past, especially in the x-ray regime where coherent imaging has stirred much interest as a way to circumvent the lack of suitable lenses [61,62,[106][107][108][109][110][111][112][113]. The rationale for measuring coherence properties in these studies is that by experimental control of the probe, spatial coherence can be increased sufficiently high to warrant that the coherence length ξ exceeds the field of view.…”

Non-equilibrium dynamics of lipid bilayers

“…Electron Laser [44] and in house x-ray sources. To achieve these goals the work was divided into three major branches of activity.…”

“…Two additional experiments related to (i) a characterization of x-ray induced radiation damage by means of a combination of high resolution diuse x-ray scattering with a scanning Kelvin-probe [43] (ii) the characterization of the single shot coherence properties of the 'FreieElektronen-Laser in Hamburg' (FLASH) third harmonic [44] have been carried out in the context of this thesis. We refer to the original publications for further details.…”