The soft X-ray and XUV split-and-delay unit at beamlines FL23/24 at FLASH2

This is the authors' abstract. We don't add key points for this paper.

A split-and-delay unit for the extreme ultraviolet and soft X-ray spectral regions has been built which enables time-resolved experiments at beamlines FL23 and FL24 at the Free-electron LASer in Hamburg (FLASH). Geometric wavefront splitting at a sharp edge of a beam splitting mirror is applied to split the incoming soft X-ray pulse into two beams. Ni and Pt coatings at grazing incidence angles have been chosen in order to cover the whole spectral range of FLASH2 and beyond, up to h ν = 1800 eV. In the variable beam path with a grazing incidence angle of ϑ d = 1.8°, the total transmission ( T ) ranges are of the order of 0.48 < T < 0.84 for h ν < 100 eV and T > 0.50 for 100 eV < h ν < 650 eV with the Ni coating, and T > 0.06 for h ν < 1800 eV for the Pt coating. For a fixed beam path with a grazing incidence angle of ϑ f = 1.3°, a transmission of T > 0.61 with the Ni coating and T > 0.23 with a Pt coating is achieved. Soft X-ray pump/soft X-ray probe experiments are possible within a delay range of −5 ps < Δ t < +18 ps with a nominal time resolution of t r = 66 as and a measured timing jitter of t j = 121 ± 2 as. First experiments with the split-and-delay unit determined the averaged coherence time of FLASH2 to be τ c = 1.75 fs at λ = 8 nm, measured at a purposely reduced coherence of the free-electron laser.