X-ray echo spectroscopy

TL;DR

X-ray echo spectroscopy is a novel technique inspired by neutron spin-echo that enhances spectral resolution and signal strength in inelastic x-ray scattering by using a time-reversal dispersing system to produce high-resolution spectra.

Contribution

The paper introduces a new x-ray echo spectroscopy method that overcomes spectral resolution and signal limitations of traditional IXS, with specific schemes for ultra-high-resolution applications.

Findings

Achieves spectral resolution of 0.02-0.1 meV with high resolving power (>10^8).

Provides over 1000-fold signal enhancement compared to traditional methods.

Applicable across different photon frequency domains.

Abstract

X-ray echo spectroscopy, a counterpart of neutron spin-echo, is being introduced here to overcome limitations in spectral resolution and weak signals of the traditional inelastic x-ray scattering (IXS) probes. An image of a point-like x-ray source is defocused by a dispersing system comprised of asymmetrically cut specially arranged Bragg diffracting crystals. The defocused image is refocused into a point (echo) in a time-reversal dispersing system. If the defocused beam is inelastically scattered from a sample, the echo signal acquires a spatial distribution, which is a map of the inelastic scattering spectrum. The spectral resolution of the echo spectroscopy does not rely on the monochromaticity of the x-rays, ensuring strong signals along with a very high spectral resolution. Particular schemes of x-ray echo spectrometers for 0.1--0.02-meV ultra-high-resolution IXS applications (resolving power $> 10^8$) with broadband $\simeq$~5--13~meV dispersing systems are introduced featuring more than $10^3$ signal enhancement. The technique is general, applicable in different photon frequency domains.