SwissFEL Instrument Bernina
The X-ray beamline design emphasizes experimental stability with state-of-the-art X-ray optical elements and single pulse diagnostics which should ensure stable FEL beam pointing and femtosecond timing over days.
A flexible diffractometer platform allows to apply different resonant and non-resonant diffraction techniques in combination with even heavy load sample environments like low temperature cryostats or magnets.
A large range from THz to UV light pulses pulses converted from a 20 mJ Ti:Sapphire laser system can be used to specifically excite specimens in pump/probe experiments.
The instrument is operated by the Bernina Group.
|Bernina endstation and X-ray parameters|
|Photon energy range||4.5 keV – 12.7 keV|
|Beam profile||Focused < 5x5 µm2 (fwhm) to unfocused ~500x500 µm2 (fwhm, photon energy dependent)|
|Bandwidth||Monochromatic (Si(111), Si(311), InSb(111) and harmonics) and pink beam (~0.25% of fundamental)|
|Environment||He or ambient atmosphere, platform for user-supplied chambers, N2 and He based cryo stream coolers down to ~80 K (tested), Vacuum chamber for low sample temperature (~5 K)|
|Sample systems||Solids: single crystals, powders, amorphous systems|
|Detectors and Spectrometer||-1.5 M Jungfrau detector
-16 M Jungfrau detector
-Diodes or single element (0.5 M) Jungfrau detectors for multi- purpose applications
|Bernina optical pump laser|
|Primary pump source||800 nm, 35 fs FWHM, 10 mJ (Ti:Sapphire)|
|Secondary pump sources||240 nm - 14 micron (OPA with additional nonlinear conversion options). At present pulse energies at the sample location for 240-400 nm have been measured in the range of 10-30 µJ. We expect pulse energies of 150-500 µJ between 400 nm and 780 nm; 150-500 µJ between 1 µm and 2.5 µm; 15-30 µJ between 2.5 µm and 14 µm. Pulse durations are expected to be approximately 50 fs fwhm and up to 250 fs for the 2.5 µm to 14 µm range depending on the wavelength. Nearly single cycle THz (~ 1THz center frequency). Preliminary commissioning measurements have measured fields of > 300 kV/cm for nearly-single-cycle pulses with a center frequency near 1 THz. Other center frequencies in the range of 1-2.5 THz are possible but not yet tested.|
Current Highlights and News
Schematic ultrafast surface diffraction setup used for monitoring the crystal lattice in multiple directions.
Supercooled water scattering signals show an anolmalous structure factor temperature dependence suggesting decreasing density at lowering temperatures below 236 K (-37°C).
This experiment performed at SwissFEL shows how fast we can localize electrons out of an electron gas into correlated, well localized states of a material. It is based on a combined ultrafast x-ray absorption and diffraction experiment on an intermetallic system.