Evidence for phonon hardening in laser excited gold using x-ray diffraction at a hard x-ray free electron laser
Data files
Jan 21, 2024 version files 7.09 GB
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FocalSpotImaging_dataset.zip
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logbook.xlsx
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README.md
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timetool_dataset.zip
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XRD_dataset.zip
Abstract
Studies of laser-heated materials on femtosecond timescales have shown that the interatomic potential can be perturbed at sufficiently high laser intensities. For gold, it has been postulated to undergo a strong stiffening leading to an increase of the phonon energies, known as phonon hardening. Despite efforts to investigate this behavior, only measurements at low absorbed energy density have been performed, for which the interpretation of the experimental data remains ambiguous. By using in situ single-shot x-ray diffraction at a hard x-ray free electron laser, the evolution of diffraction line intensities of laser-excited Au to a higher energy density provides evidence for phonon-hardening.
README
Evidence for phonon hardening in laser excited gold using x-ray diffraction at a hard x-ray free electron laser -- LCLS LW5919
This dataset contains the raw images used in the analysis for the manuscript entitles "Evidence for phonon hardening in laser excited gold using x-ray diffraction (XRD) at a hard x-ray free electron laser". The experiment was performed at the Matter in Extreme Conditions (MEC) endstation at the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory. We are including the raw images for the X-ray diffraction pattern and the images collected using the timetool available at MEC. Further details can be found in the Materials and Methods of the main manuscript.
Description of the data and file structure
We are uploading a folder containing the XRD images named "XRD_dataset" and one folder with the timetool images named "timetool_dataset". Within each folder, we have separated the data in different sub-folders for each run collected during the experiment. Each run corresponds to a nominal time delay between the X-ray pulse and the optical laser pulse. Within each run folder, the images are numbered for each X-ray pulse used.
The timetool images and the XRD images are collected simultaneously. An XRD image corresponds to a unique timetool image. For instance "XRD_dataset/r295/XRD_r295_0.tif" corresponds to "timetool_dataset/r295/TT_r295_0.tif".
We also include an image of the focal spot for r256. This run was used to define t = 0 ps between the optical laser pulse and the X-ray pulse. More details are found in the supplementary information.
For the data presented in the manuscript, we have filtered the images within each run based on the signal on the timetool. When the timetool singal could not been seen we discarded this X-ray pulse since we could not obtain a precise timing.
The timetool signal is stronger for r256 because the thickness of SiN was larger than the other runs.
Description of the logbook sheet
- Column "Run Number":
Number of folder corresponding to the same experimental conditions
- Column "Change timing based position of translation stage of timetool (MEC:LAS:MMN:19.RBV) [mm]"
When changing the time delay between the optical laser pulse and the X-ray pulse, timing on the timetool needs to be compensated by a delay stage. The values in this column report the position of the delay stage.
- Column "Change relative timing based on delay stage compared to run 256 (reference for defining t = 0ps)"
This column converts the position of the previous column into a time delay. The reference is taken to be the position of r256 which define t = 0 ps.
- Column "Laser triggering time (LAS:FS6:VIT:FS_TGT_TIME) [ns]"
These values correspond to the triggering time of the short pulse laser system.
- Column "Change relative timing on laser triggering compared to r256 Vitara [ps]"
These values calculate the triggering time from the previous column into a time delay using r256 as a reference.
- Column "Comments"
Comments for each run. The numerical values correspond to the targeted time delay for each run.
Column E corresponds to the actual time delay of the run. These values are within 0.1 ps of the targeted time delay. To reach the timing accuracy described in the main manuscript we need to use the time tool. However, as seen in column C, the time delay on the time tool doesn't match the values in column E. If we use the time tool with the pixel position found for t = 0 ps using r256 (analysis in Materials and Methods), then we would measure a time delay that is offset by the value of C-E. This offset needs to be compensated.
For run 288, only X-ray pulses were present. The optical laser was not fired so no values for columns B to E are present. We use "NA" to represent this.
Methods
The X-ray diffraction data were collected at the LCLS using an ePix10k detector. The detector was calibrated using a CeO2 calibrant. The orientation of the detector was then determined using the open source software Dioptas. The data were then corrected for polarization (the LCLS beam was vertically polarized). The edges of each detector tile were masked. The details about the extraction of the normalized intensity is found in the Materials and Methods of the manuscript.
For timing between the optical laser pulse and the X-ray pulse, we used the time tool system available at MEC. The extraction of the relative timing, determination of the absolute timing, and timing uncertainties can be found in the Materials and Methods of the manuscript.
Usage notes
No particular software is needed to open the data files. We have used Python for the data analysis.