In many single-pulse experiments of X-ray free electron lasers, the spectrum and intensity distribution of the self-amplifying spontaneous radiation beams fluctuate significantly. It is necessary to perform accurate spectral characterization of each pulse. In this paper, we present an in-line spectrometer that can observe the distribution of energy and incident intensity of single pulse X-ray photons in real time. The X-ray diffraction is achieved by using a high precision transmission crystal bending to fixed pressure bending, and the spectrum is recorded by a spatial resolution detector. At the same time, most of the incident flux is transmitted to the downstream experiment. In this paper, based on the X-ray crystal diffraction theory, geometric optical path designs were carried out, high-precision transmission curved-crystal with fixed bending was developed, the optical path of in-line transmission spectrometer was built, and the copper Kα1 and Kα2 obtained by the test were used for spectral calibration. The experimental results show that each pixel on the detector corresponds to 0.43eV, and the half-width of Kα1 is 3.44 eV. The Single-pulse spectrometer can be used for hard x-ray free electron lasers spectroscopy experiments.
Benefitting from the ultra-broad transparency window, high refractive index and exceptional thermal conductivity, diamond has attracted numerous spotlights on the optical applications and the academic researches. However, the practical deployments of high-quality diamond element were obstructed by the immature manufacture techniques. Here we designed a new mask system for diamond etching that utilizes SiO2 as the main hard mask layer and Cr as the adhesive layer. The cross-section morphology revels three distinct characteristics including an upper slope, a middle vertical sidewall and a trench at the bottom because of the retreat of thick SiO2 mask during the etching process. The completely different etching profile from the previous metal masks has the potential to realize higher aspect ratio etching than traditional metal masks for diamond elements.
As the spectrum of each pulse from XFEL (X-ray free electron lasers, XFEL) undulator (often referred as pink X-ray) varied between each other, it is necessary to measure the intensity and spectrum of each pulse. The major parameters of the spectrometer are the facet of bent crystal, the Bragg angle, the transmittance (related to the material, its thickness and transmission angle), energy range and energy resolution. An ultrathin Si wafer was put above a concave lens and under a convex lens. Bending was achieved by applying the pressure, then the Si wafer with 25μm thickness would be regularly bent onto the concave profile until the convex substrate, Si wafer and the concave lens were overlap. The cylindrical substrates were provided with holes to let the FEL beam through the crystal, and the radius of curvature could be varied from 0.2m to 1m. The crystal orientation and miscut angle were measured by a high resolution X-ray diffractometer. Finally, the energy dispersion spectra were measured by a spectrometer built in laboratory.
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