X-ray Echo Spectroscopy

• Published in: Physical review letters 2016-02, Vol.116 (8), p.080801-080801, Article 080801
• Main Author: Shvyd'ko, Yuri
• Format: Article
• Language: English
• Subjects: Asymptotic properties; Broadband; Dispersing; Inelastic scattering; Spectral resolution; Spectroscopy; X-rays
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.116.080801

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 pointlike 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 ultrahigh-resolution IXS applications (resolving power >10^{8}) with broadband ≃5-13  meV dispersing systems are introduced featuring more than 10^{3} signal enhancement. The technique is general, applicable in different photon frequency domains.