The TRIXS end-station for femtosecond time-resolved resonant inelastic x-ray scattering experiments at the soft x-ray free-electron laser FLASH

Abstract

We present the experimental end-station TRIXS dedicated to time-resolved soft x-ray resonant inelastic x-ray scattering (RIXS) experiments on solid samples at the free-electron laser FLASH. Using monochromatized ultrashort femtosecond XUV/soft x-ray photon pulses in combination with a synchronized optical laser in a pump-probe scheme, the TRIXS setup allows measuring sub-picosecond time-resolved high-resolution RIXS spectra in the energy range from 35 eV to 210 eV, thus spanning the M-edge (M 1 and M 2,3 ) absorption resonances of 3d transition metals and N 4,5 -edges of rare earth elements. A Kirkpatrick–Baez refocusing mirror system at the first branch of the plane grating monochromator beamline (PG1) provides a focus of (6 × 6) μ m 2 (FWHM) at the sample. The RIXS spectrometer reaches an energy resolution of 35–160 meV over the entire spectral range. The optical laser system based on a chirped pulse optical parametric amplifier provides approximately 100 fs (FWHM) long photon pulses at the fundamental wavelength of 800 nm and a fluence of 120 mJ/cm 2 at a sample for optical pump-XUV probe measurements. Furthermore, optical frequency conversion enables experiments at 400 nm or 267 nm with a fluence of 80 and 30 mJ/cm 2 , respectively. Some of the first (pump-probe) RIXS spectra measured with this setup are shown. The measured time resolution for time-resolved RIXS measurements has been characterized as 287 fs (FWHM) for the used energy resolution.

URSA-PQ: A Mobile and Flexible Pump-Probe Instrument for Gas Phase Samples at the FLASH Free Electron Laser

“…The discrepancy could possibly be attributed to a higher jitter compared to past experiments and longer term drifts. , where is the UV pulse length, the X-ray pulse length, the intra-train jitter of the X-ray pulses within the macro-bunch, the intra-train jitter of the UV pulses within the macrobunch and the relative timing jitter of X-ray and UV laser pulses [36]. The UV pulse duration has been determined to be =80 fs by a frequency resolved optical gating (FROG) measurement [37].…”

New Implementation of an Equation-of-Motion Coupled-Cluster Damped-Response Framework with Illustrative Applications to Resonant Inelastic X-ray Scattering

“…An X-ray technique that has significantly benefited from the recent advances in X-ray light sources and instrumentation, in particular synchrotrons, is resonant inelastic X-ray scattering (RIXS). This technique is also known as resonant (radiative) inelastic X-ray Raman scattering. − Broadly speaking, RIXS can be regarded as a two-photon process, equivalent to vibrational Raman scattering. The first step in both processes is the absorption of a photon, for RIXS in the X-ray region (i.e., XAS), and for conventional Raman in the near-IR to UV region .…”

“…With RIXS experiments becoming more feasible and popular during the past decade, even in time-resolved regimes, the interest in theoretical approaches capable of simulating the RIXS observables has also increased, as it is deemed essential for the interpretation of the experimental spectra. − A nonexhaustive list in this regard includes methods based on the algebraic diagrammatic construction (ADC) approach, on time-dependent density functional theory (TD-DFT), ,, on multiconfigurational self-consistent field (MCSCF) and density-matrix renormalization group (DMRG) theories, and on coupled-cluster (CC) theory. − …”

The meV XUV-RIXS facility at UE112-PGM1 of BESSY II

“…Soft X-ray RIXS with a strong focus on the K-edges of nitrogen and oxygen as well as the transition metal L-edges has become a powerful experimental technique with an extensive body of work over the last 20 years (Gel'mukhanov et al, 2021;Ament et al, 2011;Savchenko et al, 2021;Schmitt et al, 2014). In contrast the XUV region ending just above the carbon K-edge (280 eV) has been much less in the focus of investigation and only very few highresolution RIXS stations exist for this energy range (Strocov et al, 2010;Yamane et al, 2013;Xue et al, 2014;Schmitt et al, 2013;Kokkonen et al, 2021;Dziarzhytski et al, 2020). In this region access to the M-edges of transition metals as well as to the N-edges of elements of the lanthanide series is possible in addition to the shallow core levels of highly important elements such as silicon, beryllium, sulfur, phosphor and carbon, to name a few.…”