This manuscript presents the first systematic study of non-periodic, broadband Mo/Si multilayer coatings with and without B
C interface barrier layers for hard x-ray applications with large field of ...view. The photon energy of operation in this work is 17.4 keV, the Mo Kα emission line. The coatings involve layers with varying thicknesses in the nanometer scale and the behavior at the layer interfaces plays a crucial role in their performance. Reflectivity measurements and modeling at 8.05 keV and 17.4 keV, Transmission Electron Microscopy (TEM), as well as thin film stress measurements, are employed to examine and optimize the reflective performance of these coatings and the physics of their constituent layers and interfaces. Mo/Si with B
C barrier layers on the Mo-on-Si interface is shown to produce the highest reflectivity among all design configurations considered in this work.
In this work we point out that slope errors play only a minor role in the performance of a certain class of x-ray optics for X-ray Free Electron Laser (XFEL) applications. Using physical optics ...propagation simulations and the formalism of Church and Takacs Opt. Eng. 34, 353 (1995), we show that diffraction limited optics commonly found at XFEL facilities posses a critical spatial wavelength that makes them less sensitive to slope errors, and more sensitive to height error. Given the number of XFELs currently operating or under construction across the world, we hope that this simple observation will help to correctly define specifications for x-ray optics to be deployed at XFELs, possibly reducing the budget and the timeframe needed to complete the optical manufacturing and metrology.
In this work we have developed aperiodic Molybdenum/Silicon (Mo/Si) multilayers (MLs) to reflect 16.25 keV photons at a grazing angle of incidence of 0.6° ± 0.05°. To the best of our knowledge this ...is the first time this material system has been used to fabricate aperiodic MLs for hard x-rays. At these energies new hurdles arise. First of all a large number of bilayers is required to reach saturation. This poses a challenge from the manufacturing point of view, as thickness control of each ML period becomes paramount. The latter is not well defined a priori, due to the thickness of the interfacial silicide layers which has been observed to vary as a function of Mo and Si thickness. Additionally an amorphous-to-crystalline transition for Mo must be avoided in order maintain reasonably low roughness at the interfaces. This transition is well within the range of thicknesses pertinent to this study. Despite these difficulties our data demonstrates that we achieved reasonably flat ML response across the angular acceptance of ± 0.05°, with an experimentally confirmed average reflectivity of 28%. Such a ML prescription is well suited for applications in the field of hard x-ray imaging of highly diverging sources.
Numerical simulations of the current and future pulse intensity distributions at selected locations along the Far Experimental Hall, the hard X‐ray section of the Linac Coherent Light Source (LCLS), ...are provided. Estimates are given for the pulse fluence, energy and size in and out of focus, taking into account effects due to the experimentally measured divergence of the X‐ray beam, and measured figure errors of all X‐ray optics in the beam path. Out‐of‐focus results are validated by comparison with experimental data. Previous work is expanded on, providing quantitatively correct predictions of the pulse intensity distribution. Numerical estimates in focus are particularly important given that the latter cannot be measured with direct imaging techniques due to detector damage. Finally, novel numerical estimates of improvements to the pulse intensity distribution expected as part of the on‐going upgrade of the LCLS X‐ray transport system are provided. We suggest how the new generation of X‐ray optics to be installed would outperform the old one, satisfying the tight requirements imposed by X‐ray free‐electron laser facilities.
Numerical simulations of the current and future pulse intensity distributions at selected locations along the hard X‐ray section of the Linac Coherent Light Source are provided. Estimates are given for the pulse fluence, energy and size in and out of focus, taking into account effects due to the experimentally measured divergences of the X‐ray beam, and measured figure errors of all X‐ray optics in the beam path.
We study an effective spin model derived perturbatively from a random transverse-field Ising model on the pyrochlore lattice. The model consists of spin configurations on the pyrochlore lattice, ...restricted to the spin-ice subspace, with spins interacting with random Ising exchange couplings as well as ring exchanges along the hexagons of the lattice. This model is studied by exact diagonalization up to N=64 site systems. We calculate spin-glass correlation functions and local entanglement entropy ST between spins in a single tetrahedron and the rest of the system. We find that the model undergoes two phase transitions. At weak randomness the model is in a quantum spin-ice phase where ST=ln6. Increasing randomness, at low transverse fields, first leads to a frozen phase, with long-range spin-glass order and ST=ln2 corresponding to the Cat states associated with Ising order. Further increase in randomness leads to a random resonating-hexagon phase with a frozen backbone of spins and a broad distribution of entanglement entropies. The implications of these studies for non-Kramers rare-earth pyrochlores are discussed.
We use numerical linked cluster expansions (NLC) and exact diagonalization to study confinement transitions out of the quantum spin liquid phase in the pyrochlore-lattice Ising antiferromagnet with ...random transverse fields. We calculate entanglement entropies associated with local regions defined by single tetrahedron to observe these transitions. The randomness-induced confinement transition is marked by a sharp reduction in the local entanglement and a concomitant increase in Ising correlations. In NLC, it is studied through the destruction of loop resonances due to random transverse-fields. The confining phase is characterized by a distribution of local entanglement entropies, which persists to large random fields.
We study an effective spin model derived perturbatively from random transverse-field Ising model on the pyrochlore lattice. The model consists of spin-configurations on the pyrochlore lattice, ...restricted to the spin-ice subspace, with spins interacting with random Ising exchange couplings as well as ring exchanges along the hexagons of the lattice. This model is studied by exact diagonalization upto N=64 site systems. We calculate spin-glass correlation functions and local entanglement entropy \(S_T\) between spins in a single tetrahedron and the rest of the system. We find that the model undergoes two phase transitions. At weak randomness the model is in a quantum spin-ice phase where \(S_T=\ln{6}\). Increasing randomness first leads to a frozen phase, with long-range spin-glass order and \(S_T=\ln{2}\) corresponding to the Cat states associated with Ising order. Further increase in randomness leads to a random resonating-hexagon phase with a frozen backbone of spins and a broad distribution of entanglement entropies. The implications of these studies for non-Kramers rare-earth pyrochlores are discussed.
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