Scientific Instrument FXE

The FXE instrument will enable ultrafast pump–probe experiments on ultrafast timescales—below 100 femtoseconds—for a broad scientific user community.

The instrument comprises two independent secondary X-ray emission spectrometers next to a 1-Mpx detector for scattering studies. Its main research is devoted to dynamic studies of chemical and biochemical reactions in liquids next to different solid-state applications. With a powerful laser as pump source, it will permit studies with femtosecond time resolution exploiting different observables via a suite of hard X-ray tools (which may be further expanded over time):

  • X-ray diffraction (XRD)
  • X-ray diffuse scattering (XDS), or wide-angle X-ray scattering (WAXS)
  • X-ray emission spectroscopies (XES): non-resonant, or resonant inelastic X-ray scattering (RIXS)
  • X-ray absorption spectroscopies: X-ray absorption near-edge structure (XANES), or extended X-ray absorption fine structure (EXAFS)

The FXE scientific instrument will serve a broad scientific community and will embrace several fields of ultrafast X-ray science and their applications. State-of-the-art femtosecond instrumentation and techniques, both for X-rays and optical lasers, will deliver new information about geometric and electronic structures serving applications in many fields, and particular in the areas of

  • Chemical dynamics
  • Photovoltaic applications
  • Photosynthesis
  • Catalytic processes
  • Material physics

Operation of the FXE instrument is planned to start in 2017. A more detailed description of the science case of FXE can be found in the FXE TDR and CDR.

The main specifications and beam parameters of FXE are summarized in table 1 below. Further technical details about the available equipment at FXE is available here and in the TDR and CDR or by contacting the FXE group.

Full instrument specifications (see here for early user specifications)

Bandwidth ΔE/E

1x10-3 (natural FEL source) , 1x10-4 (standard Si(111) 4-bounce mono)

Photon energy range

5–20 keV


Linear (horizontal), circular (future option)

X-ray pulse duration

1–300 fs FWHM

Beam size

1–300 µm adjustable (via several Be lenses)

Special optics

1 primary 4-bounce Si(111) mono
2 secondary (von Hamos, Johann) spectrometers

Optical laser wavelengths

Pump–probe (0.1–1 mJ) 800 nm (15–100 fs)
Pump–probe (1 µJ) 1030 nm (275 fs) NOPA adjustable UV-vis-NIR (10 fs possible)
Pump–probe (>20 mJ) 1030 nm (850 fs)
Pump–probe (>50 µJ) 1 mm (=0.3 THz) generated via optical rectification

X-ray detectors

APD (0D, full rep. rate with MHz DAQ)
Gotthard (1D, 1280 px, 50 µm pixel pitch, 0.9 MHz)
LPD (2D, 1 Mpx, (500 µm)² pixel size, 512 frames at 4.5 MHz, 3-fold dynamic gain covering 1 (SP at 12keV) to 1x105 per pixel)