High-contrast sub-millivolt inelastic X-ray scattering for nano- and mesoscale science

Abstract

Photon and neutron inelastic scattering spectrometers are microscopes for imaging condensed matter dynamics on very small length and time scales. Inelastic X-ray scattering permitted the first quantitative studies of picosecond nanoscale dynamics in disordered systems almost 20 years ago. However, the nature of the liquid-glass transition still remains one of the great unsolved problems in condensed matter physics. It calls for studies at hitherto inaccessible time and length scales, and therefore for substantial improvements in the spectral and momentum resolution of the inelastic X-ray scattering spectrometers along with a major enhancement in spectral contrast. Here we report a conceptually new spectrometer featuring a spectral resolution function with steep, almost Gaussian tails, sub-meV (≃620 μeV) bandwidth and improved momentum resolution. The spectrometer opens up uncharted space on the dynamics landscape. New results are presented on the dynamics of liquid glycerol, in the regime that has become accessible with the novel spectrometer.

X-ray Echo Spectroscopy

“…Such components have been experimentally demonstrated recently [8,14]. Implementation of x-ray echo spectrometers is, therefore, realistic.…”

“…Laterally graded multilayer Montel mirrors recently proved to be useful exactly in this role [14,21].…”

“…Therefore, optical designs of the dispersing elements have to be found featuring both large D ∪ and ∆E ∪ . Figures 3 and 4 show representative examples of multi-crystal CDDWtype inline dispersing elements [14][15][16] of the defocusing and refocusing systems, respectively, with the required cumulative dispersion rates, asymmetry factors, and with bandwidths ∆E ∪ 5.5−9 meV, i.e., ∆E ∪ /∆ε 55−90, designed for use with 9.1-keV photons. These examples are modifications of the dispersing elements designs presented in [9].…”

“…This is a hard x-ray analog of the optical diffraction gratings or optical prisms. A large dispersion rate is a key for achieving high spectral resolution in angular-dispersive x-ray spectrometers [9,14], including echo spectrometers, see Eq.…”

“…In-line four-crystal CDDW-type dispersing optics [14][15][16] D 2 ), and wavelength-selecting (W) crystals, which can be arranged in different scattering configurations. In a general case, the scattering configuration is defined as (φ 1 s 1 , φ 2 s 2 , φ 3 s 3 , φ 4 s 4 ).…”