Scientific Instrument FXE

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

The instrument comprises two independent X-ray emission spectrometers that can be used simultaneously with a large-area 1 Megapixel detector for scattering studies. Our primary trigger for these measurements is an ultrafast, tunable laser, allowing excitation wavelengths from the UV to the IR to be used. FXE's research focus is on measuring ultrafast dynamics in the condensed phase using a broad range of hard X-ray techniques. This covers research fields as divers as ultrafast chemical and biochemical dynamics of solution-phase samples, solid-state condensed matter physics and nonlinear X-ray techniques. Techniques that have been demonstrated at FXE include:

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 spectroscopy (XAS)

General capabilities of FXE offered for Users in this call

The FXE instrument enables 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 permits 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 serves a broad scientific community and embraces 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, delivers 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 started in September 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.

Instrument specifications

for past User Experiments

Capabilities of FXE offered for Users in 14th call for proposals

Deadline June 24, 2025 at 16:00 CEST

Bandwidth ΔE/E	1x10^-3 (natural SASE bandwidth) , 1x10^-4 (Si(111) 2-bounce mono)
Photon energy range	4.6–22 keV
Polarization	Linear (horizontal)
X-ray pulse duration	50 fs FWHM Shorter pulses (< 10 fs) are possible from the accelerator, please contact us for further discussions
Beam size	8–200 µm adjustable (via several Be lenses)
Special optics	1 primary 4-bounce Si(111) mono (generally used in a two bounce geometry) 3 secondary spectrometers (von Hamos, Johann, Dumond/Laue geometries)
Optical laser wavelengths	800 nm fundamental wavelength with up to 1 mJ (15 or 50 fs mode) 1030 nm fundamental wavelength with up to 20 mJ (850 fs) Standard configuration: parallel delivery of 800/400/266 nm harmonics branch and TOPAS OPA branch using 50 fs PP laser mode and 282 kHz repetition rate Harmonics branch: Pump–probe (200 µJ) 800 nm (50 fs, 15 fs possible), (20 uJ) 400 nm (50 fs, 15 fs possible), (5 uJ) 266 nm (50 fs, 15 fs possible) @ 282 kHz TOPAS OPA branch: (1-5 uJ) 240-400 nm (50 fs), (1-20 uJ) 400-1000 nm (50 fs), (2.5-60 uJ) 1-2.5 um (50 fs), (1-5 uJ) 2.5-5 um @ 282 kHz THz source: >5 µJ @ 1.0 THz generated via BNA organic crystal (~1 MV/cm field strength with 200 um focus using off-axis parabolic mirrors)
X-ray detectors	APD (0D, full repetition rate with MHz DAQ) Si diodes of various sizes (0D, full repetition rate with MHz DAQ) Gotthard 2 (1D, 1280 px, gain switching, 50 µm pixel pitch, up to 1.1 MHz) Jungfrau 1M & 500k (2D, gain-switching, 75 x 75 µm pixel size, 10 Hz) LPD (2D, 1 Mpx, (500 µm)³ pixel size, 512 frames at 4.5 MHz, 3-fold dynamic gain covering 1 (SP at 12keV) to 1x10⁴ per pixel)