James M. Ablett

X-ray cavity quantum optics with inner-shell transitions has been limited by the spectral overlap between resonant and continuum states. Here, we report the first experimental demonstration of cavity-controlled core-to-core resonant inelastic x-ray scattering (RIXS). We suppress the absorption-edge effects by monitoring the RIXS profile, thereby resolving the resonant state from the overlapping continuum. We observe distinct cavity-induced energy shifts and cavity-enhanced decay rates in the 2 p 3 d RIXS spectra of WSi 2 . These effects, manifesting as stretched or shifted profiles in the RIXS planes, enable novel spectroscopic applications via cavity-controlled core-hole states. Our results establish core-to-core RIXS as a powerful tool to manipulate inner-shell dynamics in x-ray cavities, offering new avenues for integrating quantum optical effects with x-ray spectroscopy.

In this combined experimental and theoretical work, we present state-of-the-art liquid jet experiments based on x-ray emission spectroscopy of the [Fe(CN)6]4− and [Fe(CN)6]3− molecular ions in the hard-x-ray energy range. The ab initio simulations of the valence-to-core and Kβ spectra reveal insights into the valence and metal’s d-shells, respectively. These results open new perspectives for applying spectroscopy to organometallic complexes in order to disentangle and probe various environmental effects, including solvent interactions, pH variations, and ligand field influences and dynamical processes, such as charge transfer or photoinduced ligand exchange reactions such as photoaquation in solution.

We propose and demonstrate a method to manipulate x-ray emission rates and directions by coupling them to surface plasmon polaritons via x-ray-to-ultraviolet down-conversion in a metal. This mechanism generates highly correlated photon pairs, each consisting of one x-ray and one ultraviolet photon, enabling fine control of x-ray angular and spectral characteristics through the ultraviolet photons resonant with the surface plasmons. Our approach bridges a previously insurmountable gap between x-ray and plasmonic energy and momentum, enabling the use of engineered plasmonic structures to control x-ray emission. Furthermore, our work unlocks opportunities to explore plasmonic physics at the microscopic scale with atomic-scale resolution.

We present the design and performance of a new multi-crystal x-ray emission spectrometer installed at the GALAXIES beamline at Synchrotron SOLEIL. The new instrument, which we name “MULTIXS,” can host up to five analyzer crystals and supersedes our previous XES spectrometer design, providing a compact, simple design with all the analyzer crystals contained in the horizontal sample plane. This feature provides a direct view of the sample area and avoids the potential masking of the sample for constrained sample environments. This new design allows for the use of both 0.5 m and 1 m radius spherical analyzer crystals. In addition, the ability to continuously scan the spectrometer energy provides relatively fast scanning with high quality emission data and minimum dead-time overhead.

Synchrotron radiation facilities provide highly polarized x-ray beams across a wide energy range. However, the exact type and degree of polarization vary according to the beamline and experimental setup. To accurately determine the angle and degree of linear polarization, a portable x-ray polarimeter has been developed. This setup consists of a silicon drift detector that rotates around a target made of high-density polyethylene. The imprint generated in the angular distribution of scattered photons from the target at a 90-degree angle between the incident x-rays and detector has been exploited to determine the beam polarization. Measurements were conducted at the GALAXIES beamline of the SOLEIL synchrotron. The expected angular distribution of the scattered photons for a given beam polarization was obtained through simulations using the Geant4 simulation toolkit. An excellent agreement between simulations and the collected data has been obtained, validating the setup and enabling a precise determination of the beam polarization.

GALAXIES is an in-vacuum undulator hard X-ray micro-focused beamline dedicated to the study of the electronic structure of materials with high energy resolution using both photoelectron spectroscopy and inelastic X-ray scattering and under both non-resonant (NR-IXS) and resonant (RIXS) conditions. Due to the penetrating power of hard X-rays and the `photon-in/photon-out' technique, the sample environment is not a limitation. Materials under extreme conditions, for example in diamond anvil cells or catalysis chambers, thus constitute a major research direction. Here, the design and performance of the inelastic X-ray scattering end-station that operates in the energy range from ∼4 keV up to 12 keV is reported, and its capabilities are highlighted using a selection of data taken from recently performed experiments. The ability to scan `on the fly' the incident and scattered/emitted X-ray energies, and the sample position enables fast data collection and high experimental throughput. A diamond X-ray transmission phase retarder, which can be used to generate circularly polarized light, will also be discussed in the light of the recent RIXS–MCD approach.

(2018). HAXPES for Materials Science at the GALAXIES Beamline. Synchrotron Radiation News: Vol. 31, No. 4, pp. 4-9.