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The CLÆSS beamline is providing a simultaneous and unified access to two complementary techniques: X-ray absorption and emission spectroscopes. The incoming energy range is 2.4 – 63.2 keV.  The outcoming energy range selectable by CLEAR spectrometer is 6.4 - 12.5 keV.

The sample set-ups give access to low/high-temperature (10-320 K, 80-1000 K), low/high-energy measurements (in transmission and fluorescence mode), "in situ" solid-gas reactors

A chemical laboratory in close proximity to the beamline (glove box, pellet press, fume cupboards, analytical balance etc.) is also available.

Further information is available in the following paper.



X-Ray absorption in Transmission and Fluorescence mode (silicon-drift and CdTe single channel fluorescence detector) has been in operation since 2013. 

X-Ray emission (CLEAR spectrometer) is operational since 2016 (Si(111) dynamical bent diced analyser crystal).

Beam size from 100x200 µm2 to 1x10 mm2, stable in position within ± 15µm2. Possibility to reduce the beam size by means of a pinhole with the constraints to work in air.


Multichannel Silicon-drift fluorescence detector under development. In commissioning since April 2017.

Continuos flow liquid cell under development. In commissioning since March 2017.

Integration of the pinhole in vacuum under development.

CLEAR Si(220) dynamical bent diced analyser crystal under construction.


SOURCE: Multipole Wiggler


Total length 1 m 
Period 80 mm
Number of periods 12
Minimum gap 12.5 mm
K Max 13
Maximum field  1.74 T
Critical energy 10.4 keV
Total power at minimum gap 1.7 kW @ 100 mA
4.3 kW @250 mA
6.9 kW @400 mA 
Power in 1.5 h × 0.25v mradat minimum gap 0.5 kW @100 mA
1.3 kW @250 mA
2.1 kW @400 mA



Energy range (keV)Filter thickness* CM stripeMirror angle (mrad)DCM crystalsFM toroidBeam size at sample FWHM (hor x ver)**Flux at sample (ph/sec) at 100 mA
2.4-7 - Si 4.7 Si(111) Rh 206×56 µm2 1·1013 @7 keV
6-15 57 µm Rh 4.7 Si(111) Rh 208×53 µm2 1·1013 @9 keV
7-20 0.7 µm Rh 3.3 Si(311) Rh 8×0.4 mm2 1·1012 @18 keV
14-20  0.7 µm Pt 2.4 Si(311) Pt 225×56 µm2 1·1012 @18 keV
18-35 1.5 µm Pt 2.4 Si(311) Pt 8×0.4 mm2 5·1011 @30 keV





Mask   1.5 h × 0.25 v mrad2
Low - E filters 4 filters of different thicknesses.
Collimating mirror (CM) Silicon, slot cooling with liquid Ga bath,
Si, Rh, Pt stripes, with bender.
Double crystal monochromator (DCM) Direct drive motor (= fast)
LN2-cooled (both crystals)
Si111 and Si311 pairs
Flat crystals, piezo on 2nd
Focusing mirror (FM) Pt-coated and Rh-coated double toroid 
on a single ULE® glass substrate with bender.

Core Level Emission Analyzer and Reflectometer (CLEAR) 

The instrument, that has been engineered in-house and manufactured partially-in house and by local companies, allows to energy-analyze the emitted fluorescence and to resolve with good energy resolution the signals from the different de-excitation channels. Thanks to the combined use of a Mythen unidimensional detector and a silicon diced analyzer, it permits the acquisition of the spectrum on a single-shot basis.

It gives access to all the complementary information obtainable by investigating the atomic emission lines and, the rather XAS featureless spectra, obtained with the conventional energy integrated mode, become spectra with fine structure containing key information on electronic levels and magnetic properties. 


Figure shows on the left a sketch of the CLEAR spectrometer with, at the lower right, a picture of the presently operating Si(1,1,1) dynamically bent diced analyzer. This instrument is foreseen to work, like the other existing emission spectrometer, in Rowland circle geometry, but, differently from the others, to cover continuously between 2 and 22 keV by means of 4 analyzer crystals (with different crystals reflections) in fully back of forward scattering geometries, exploiting a working wide Bragg angular range (30°-80°). The energy resolution and photon intensity (focal properties) are ensured by the diced analyzer and the analyzer dynamical sagittal bending. While only the Si(1,1,1) analyzer reflection is at the moment available, other analyzers are underway starting from the Si(2,2,0) reflection.


While figure above (right) reports an example of recently measured Co Kβ emission lines, this figure shows an example of high resolution absorption spectra collected by selecting the Co Kβ1,3 emission energy and scanning the incoming energy across the Co K-edge. The combination of a unidimensional detector and a diced analyzer permitted the acquisition of the emission spectrum during the incoming energy scan on a single-shot basis (inset in figure: 2D plot representing the spectral intensity as a function of the emitted (or transferred) and incoming photon energy across the absorption pre-peak). The 2D plots reveal two different final states, not detectable by the classical XAS.


Compatible with common “in situ” cells and cryostats. Fluorescence is collected in a back-scattering direction. As a result: a) no additional side window is required in an in situ cell or a cryostat, which means a simplified cell design with more uniform heating (cooling) and b) there is no depth-related fluorescence source broadening as with the usual 45º incidence, which means a better energy resolution.

Acquisition. The geometry allows energy dispersive images in two scales: some eV (due to diced crystal) and some hundreds of eV (due to in-Rowland circle position of the sample). Outgoing energy scans will allow the investigation of wider energy ranges.

In situ change of crystals3 Johansson-like diced Si crystals: (111), (220) and (400) split into two halves with (1.2 – 1.5 mm2) facets. The crystals cover the energy range 2 – ~28 keV (θ = 35–80º) with energy resolution better than the width of the corresponding Kα lines.

Serves for RIXS, reflectometry and polarimetry. The movable tank allows for insertion of large sample infrastructures (magnet, cryostates, chemical cells), enables completely windowless operation and also allows the use of the spectrometer as a reflectometer and polarimeter.


Below, a picture of the standard sample setup in the CLÆSS experimental hutch (left). The path of the X-ray beam is indicated together with the sample insertion apertures for the different standard setups. Pictures and caracteristics of the different standard and no-standard available setups with the sketch of the ones currently under developments (right).