Shot-by-shot characterization of focused X-ray free electron laser pulses

Abstract

X-ray free electron lasers (XFEL) provide intense and almost coherent X-ray pulses. They are used for various experiments investigating physical and chemical properties in materials and biological science because of their complete coherence, high intensity, and very short pulse width. In XFEL experiments, specimens are irradiated by XFEL pulses focused by mirror optics. The focused pulse is too intense to measure its coherence by placing an X-ray detector on the focal spot. Previously, a method was proposed for evaluating the coherence of focused pulses from the visibility of the diffraction intensity of colloidal particles by the speckle visibility spectroscopy (SVS). However, the visibility cannot be determined exactly because the diffraction intensity is integrated into each finite size detector pixel. Here, we propose a method to evaluate the coherence of each XFEL pulse by using SVS in combination with a theory for exact sampling of the diffraction pattern and a technique of multiplying the diffraction data by a Gaussian masks, which reduces the influence of data missing in small-angle regions due to the presence of a direct beamstop. We also introduce a method for characterizing the shot-by-shot size of each XFEL pulse by analysing the X-ray irradiated area.

Methods and application of coherent X-ray diffraction imaging of noncrystalline particles

“…6c). As demonstrated in our previous study, the focused Xray pulses displayed almost complete spatial coherence (Kobayashi et al 2018a).…”

“…In Japan, diffraction apparatus (Takayama and Nakasako 2012;Nakasako et al 2013;Kobayashi et al 2016aKobayashi et al , 2018b, experimental procedures (Takayama and Nakasako 2012;Kobayashi et al 2016bKobayashi et al , 2018a, data processing (Sekiguchi et al 2014a, b), and protocol for structure analyses (Sekiguchi et al 2016(Sekiguchi et al , 2017Yoshidome et al 2015;Oroguchi et al 2018) have been developed originally for structure analyses of biological specimens in the last decade. Cryogenic cXDI using X-rays from a synchrotron facility has demonstrated the potential to visualize biological cells at resolutions of several tens of nanometers (Kobayashi et al 2018b).…”

Growth of Cuprous Oxide Particles in Liquid-Phase Synthesis Investigated by X-ray Laser Diffraction

“…We used focused XFEL pulses with a 10 fs duration, which were provided at a repetition rate of 30 Hz. They had almost complete spatial coherence and an ultimately strong intensity (more than 10 10 X-ray photons/4 μm 2 /pulse) at a photon energy of 5.5 keV (X-ray wavelength of 0.225 nm). Although a focused XFEL pulse destroys a specimen particle at the atomic level, diffraction occurs from the particle before its destruction, as demonstrated by a crystal structure analysis of a protein complex by using XFEL pulses at BL3 of SACLA .…”

Coherence and pulse duration characterization of the PAL-XFEL in the hard X-ray regime

“…Such technique was successfully used to evaluate the coherence properties of other hard X-ray FELs such as LCLS 22,23 and SACLA 24 for which the degree of the transverse coherence was measured to be 0.94 ± 0.03 at 8.96 keV and 0.79 ± 0.09 at 8.0 keV, respectively. However, a recent SACLA study 27 which accounts for the exact sampling of coherent diffraction patterns in combination with recovering missing parts of the diffraction data by multiplying with a Gaussian mask, obtained a degree of coherence of 0.997 ± 0.001 at 5.5 keV. Similar corrections involving the speckle size have also been done in laser speckle contrast analysis 28 .…”