Recent Developments of the VOXES Von Hamos X-ray Spectrometer for Laboratory XES and XAS Studies

TL;DR

The paper addresses the need for high-resolution, lab-scale X-ray spectroscopy for XES and XAS by presenting VOXES, a compact Von Hamos WD-XRF spectrometer augmented with an ED-XRF line, a liquid-sample holder, and a switchable transmission-mode capability. The approach combines curved mosaic HAPG crystals, motorized positioning, and parallel detection to deliver sub-$10$ eV resolution across $5$--$20$ keV with extended/dilute samples, and to enable simultaneous WD and ED measurements. Key contributions include the integration of an ED-XRF flux-monitoring line, a dedicated liquid-sample holder, and a Y-shaped geometry that enables XAS transmission measurements on the same platform. The work demonstrates improved workflow, automation, and versatility for table-top laboratory X-ray spectroscopy, with practical impact for XES/XAS studies of materials, chemistry, and related fields.

Abstract

VOXES is a Von Hamos X-ray spectrometer developed at the INFN National Laboratories of Frascati for high-resolution laboratory X-ray spectroscopy in the 5--20~keV range. It uses curved mosaic crystals and motorized positioning stages to perform wavelength-dispersive X-ray fluorescence (WD-XRF) with sub-10~eV tunable resolution for extended and dilute samples. Recent developments include the integration of an energy-dispersive X-ray fluorescence (ED-XRF) line based on a silicon pin-diode detector, which enables flux monitoring and simultaneous ED and WD measurements. In addition, a dedicated liquid-sample holder has been introduced, and a Y-shaped support geometry, crucial for switching to a transmission layout, provides mechanical compatibility with laboratory XAS, now under implementation. These upgrades expand the versatility and automation of VOXES, strengthening its role as a table-top platform for laboratory X-ray spectroscopy.

Figures (4)

• Figure 1: The VOXES experimental setup. The X-ray tube on the left directs the beam onto the sample holder. After emission, the beam is conditioned by adjustable slits and motorized stages to ensure precise alignment. The resulting X-rays are diffracted by the mosaic crystal and subsequently detected by the position detector placed on the right.
• Figure 2: VOXES spectrometer in transmission (left) and emission (right) modes. In transmission mode, the beam passes through the sample for XAS measurements. In emission mode, the emitted X-rays are detected for XES analysis. The setup allows switching between the two modes by rotating the source and detector assemblies.
• Figure 3: WD-XRF Spectrum of a FeCoNi foil (left) used to align and calibrate with cobalt and iron reference line. Spectra (right) of high-spin K$_4$FeCN$_6$ (blue) and low-spin FeSO$_4$ (orange). The Fe K$\beta^\prime$ suppression in low-spin compounds is clearly resolved, indicating sufficient sensitivity for chemical-state analysis.
• Figure 4: Teflon liquid-sample holder used for solution measurements. The liquid is contained in a flexible pouch fixed with Teflon screws to prevent metal contamination, and sealed with a Kapton window to ensure X-ray transmission.