Speaker
Description
Optical laser speckle correlation techniques opened up the possibility of studying diffusive dynamics in randomly distributed systems. Thanks to the improvement of large-scale X-ray generation facilities, a high flux of coherent X-rays enables us to collect a sufficient intensity of X-ray speckle images and has extended the spatial resolution to atomic scales [1]. Conventional X-ray Photon Correlation Spectroscopy (XPCS) which is one of the most powerful and convenient techniques, has been widely employed to investigate the dynamics in atomic and molecular scales[2]. As the temporal resolution is defined by the collected number of speckle patterns in a time, comparably slow systems are intensively investigated due to the lower working repetition rate of X-ray area detectors in the past two decades[3]. Recently, new advanced detector technology has begun to offer and demonstrate X-ray area detectors with MHz frame rates, such as Adaptive Gain Integrated Pixel Detector (AGIPD)[4,5]. The AGIPD was initially designed for the European X-ray Free Electron Laser (E-XFEL), delivering hard X-ray pulses up to a 4.5 MHz frame rate. An alternative speckle correlation technique to investigate beyond faster dynamics than both X-ray pulse repetition rate and detector frame rate is Double Pulse X-ray Photon Correlation Spectroscopy (DP-XPCS). The DP-XPCS evaluates a speckle contrast of an image accumulated of two individual X-ray speckle patterns, and the temporal separation of two patterns corresponds to the temporal resolution. In order to accumulate two speckle patterns in a single frame, two coherent X-ray pulses are provided in a special operation mode of linear accelerators of XFEL or X-ray Split and Delay line (SDL) [6]. The SDL divides an X-ray pulse into two pulses and combines after two different beam trajectories. The precise adjustment of the path-length difference in the SDL defines the time delay with a precision down to a few fs. Here, we present the current effort in investigating ultrafast dynamics based on the speckle correlation techniques at the Materials Imaging and Dynamics (MID) beamline at E-XFEL [7]. The scope of the MID is material science experiments using the unprecedented coherent properties of the X-ray laser beams of the E-XFEL. The extremely brilliant and highly coherent X-rays with AGIPD and SDL provide the opportunity to investigate dynamics in disordered systems down to atomic length scales, with timescale ranging from femtoseconds to seconds.
References
[1] S. O. Hruszkewycz, et al., “High contrast x-ray speckle from atomic-scale order in liquids and glasses”, Phys. Rev. Lett. 109(18), 185502 (2012).
[2] G. Grübel, et al., “Correlation spectroscopy with coherent x-rays”, J. Alloys Compd. 362(1-2), 3–11 (2004).
[3] B. Ruta, et al., “Atomic-scale relaxation dynamics and aging in a metallic glass probed by X-ray photon correlation spectroscopy”, Phys. Rev. Lett. 109(16), 165701 (2012).
[4] F. Lehmkühler, et al., “Dynamics of soft nanoparticle suspensions at hard X-ray FEL sources below the radiation-damage threshold”, IUCrJ 5(6), 801–807 (2018).
[5] W. Jo, et al., “Nanosecond X-ray photon correlation spectroscopy using pulse time structure of a storage-ring source”, IUCrJ 8(1), 124–130 (2021).
[6] W. Roseker, et al., “Towards ultrafast dynamics with split-pulse x-ray photon correlation spectroscopy at free electron laser sources”, Nat. Commun.
9(1), 1704 (2018).
[7] A. Madsen et al., “Materials Imaging and Dynamics (MID) instrument at the European X-ray Free-Electron Laser Facility”, J. Synchrotron Radiat. 28, 637 (2021)
| Keywords | XFEL, X-ray speckle, XPCS, dynamics |
|---|
