Resonant inelastic x-ray scattering in warm-dense Fe compounds beyond the SASE FEL resolution limit
Communications Physics Nature Research 7:1 (2024) 266
Abstract:
Resonant inelastic x-ray scattering (RIXS) is a widely used spectroscopic technique, providing access to the electronic structure and dynamics of atoms, molecules, and solids. However, RIXS requires a narrow bandwidth x-ray probe to achieve high spectral resolution. The challenges in delivering an energetic monochromated beam from an x-ray free electron laser (XFEL) thus limit its use in few-shot experiments, including for the study of high energy density systems. Here we demonstrate that by correlating the measurements of the self-amplified spontaneous emission (SASE) spectrum of an XFEL with the RIXS signal, using a dynamic kernel deconvolution with a neural surrogate, we can achieve electronic structure resolutions substantially higher than those normally afforded by the bandwidth of the incoming x-ray beam. We further show how this technique allows us to discriminate between the valence structures of Fe and Fe2O3, and provides access to temperature measurements as well as M-shell binding energies estimates in warm-dense Fe compounds.Control of autoresonant plasma beat-wave wakefield excitation
Physical Review Research 6:1 (2024)
Abstract:
Autoresonant phase locking of the plasma wakefield to the beat frequency of two driving lasers offers advantages over conventional wakefield acceleration methods, since it requires less demanding laser parameters and is robust to variations in the target plasma density. Here, we investigate the kinetic and nonlinear processes that come into play during autoresonant plasma beat-wave acceleration of electrons, their impact on the field amplitude of the accelerating structure, and on acceleration efficiency. Particle-in-cell simulations show that the process depends on the plasma density in a nontrivial way but can be reliably modeled under specific conditions. Beside recovering previous fluid results in the deeply underdense plasma limit, we demonstrate that robust field excitation can be achieved within a fully kinetic self-consistent modeling. By adjusting the laser properties, we can amplify the electric field to the desired level, up to wave breaking, and efficiently accelerate particles; we provide suggestions for optimized laser and plasma parameters. This versatile and efficient acceleration scheme, producing electrons from tens to hundreds of MeV energies, holds promise for a wide range of applications in research industry and medicine.
Phase transitions of Fe2O3 under laser shock compression
under review for Physical Review Letters
Abstract:
We present in-situ x-ray diffraction and velocity measurements of Fe2O3 under laser shock compression at pressures between 38-116 GPa. None of the phases reported by static compression studies were observed. Instead, we observed an isostructural phase transition from α-Fe2O3 to a new α′-Fe2O3 phase at a pressure of 50-62 GPa. The α′-Fe2O3 phase differs from α-Fe2O3 by an 11% volume drop and a different unit cell compressibility. We further observed a two-wave structure in the velocity profile, which can be related to an intermediate regime where both α and α′ phases coexist. Density functional theory calculations with a Hubbard parameter indicate that the observed unit cell volume drop can be associated with a spin transition following a magnetic collapse.
Frequency chirp effects on stimulated Raman scattering in inhomogeneous plasmas
Phys. Plasmas 29, 072709 (2022)
Abstract:
On the role of bandwidth in pump and seed light waves for stimulated Raman scattering in inhomogeneous plasmas
Phys. Plasmas 29, 032102 (2022)