Single-shot spectrometer using diamond microcrystals for X-ray free-electron laser pulses

Abstract

A simple spectrometer using diffraction from diamond microcrystals has been developed to diagnose single-shot spectra of X-ray free-electron laser (XFEL) pulses. The large grain size and uniform lattice constant of the adopted crystals enable characterizing the XFEL spectrum at a resolution of a few eV from the peak shape of the powder diffraction profile. This single-shot spectrometer has been installed at beamline 3 of SACLA and is used for daily machine tuning.

Keywords: SACLA; X-ray free-electron lasers; single-shot spectrometers.

Figure 1

(a) A schematic of the spectrometer using diamond microcrystals in EH1 of SACLA BL3. (b) The energy resolution of the spectrometer evaluated with the monochromated XFEL pulses. Solid curves show expected energy resolution of the spectrometer for the case when K/D = 3.5 × 10⁻⁴ Å⁻¹ and Δθ = 150 µrad.

Figure 2

(a) Single-shot spectra of XFEL pulses measured with the spectrometer (red curves). Corresponding reflection index, pulse energy and diffraction image measured with the MPCCD detector are shown in each plot. Green curves represent average spectra of monochromated XFEL pulses (ΔE _mono/E = 1.3 × 10⁻⁴) measured with the spectrometer. (b) Histograms of photon parameters (pulse energy at the optics hutch, photon-energy spread and central photon energy) of 10 keV XFEL pulses before and after machine tuning.