The DXAS beamline is an experimental station dedicated to dispersive x-ray absorption spectroscopy (acronym for DXAS) techniques, in the hard x-ray energy range (5 to 14 keV). The peculiarity of this beamline is the capability to collect absorption spectra over an extended range of photon energies without any mechanical movement of its optical elements. The DXAS is especially suited for detecting weak signals in XANES (X-ray Absorption Near-Edge Spectroscopy) and XMCD (X-ray Magnetic Circular Dichroism) experiments and for tracking time-dependent evolution of chemical reactions.
DXAS is installed on a 1.67T bending-magnet source, and it was opened to users in 2005. The beamline is comprised by the synchrotron light source, a vertically focusing bendable mirror, a bent crystal polychromator, and an area detector. The beam path over the optical elements starts when it hits the bendable mirror, used for vertical focusing as well as harmonic rejection. Then the light beam impinges onto a polychromator bent crystal at several different incident angles, resulting in a polychromatic beam after reflection. The reflected beam is selected with a specific bandwidth of hundreds of eV, and is horizontally focused at the sample position. The transmitted signal, after the sample position, reaches an area detector. The photon energy–direction correlation is transformed into an energy–position correlation along the horizontal axis of the detector.
The main features of the beam line are fast acquisition and stability. A whole X-ray absorption spectrum is acquired in a single detector shot. Thus, it makes the technique especially useful for the study of fast processes. Due to the absence of movement of the optical elements during the data acquisition, the focused beam at the sample position is inherently stable.
The beamline has been used to support studies in the fields of materials science, solution chemistry, heterogeneous and homogeneous catalysis, electrochemistry, magnetism and geosciences.