Hard-x-ray spectrographs with resolution beyond 100μeV

Abstract

Spectrographs take snapshots of photon spectra with array detectors by dispersing photons of different energies into distinct directions and spatial locations. Spectrographs require optics with a large angular dispersion rate as the key component. In visible light optics, diffraction gratings are used for this purpose. In the hard-x-ray regime, achieving large dispersion rates is a challenge. Here we show that multicrystal, multi-Bragg-reflection arrangements feature cumulative angular dispersion rates almost two orders of magnitude larger than those attainable with a single-Bragg reflection. As a result, the multicrystal arrangements become potential dispersing elements of hard-x-ray spectrographs. The hard-x-ray spectrograph principles are demonstrated by imaging a spectrum of photons with a record high resolution of $\ensuremath{\Delta}E\ensuremath{\simeq}90$ $\ensuremath{\mu}$eV in the hard-x-ray regime, using multicrystal optics as the dispersing element. The spectrographs can boost research using inelastic ultrahigh-resolution x-ray spectroscopies with synchrotrons and seeded x-ray free electron lasers.