Snapshot of the shock wave (centre) racing through a diamond sample. The ripples on the left are caused by the edge of the sample. (Credit: Andreas Schropp/DESY)
A research team led by DESY scientists have filmed shock waves in diamonds using ultra-short pulses of X-rays opening up new possibilities for studying the properties of materials.
The extremely bright and short X-ray flashes allowed the scientists to observe the dynamic changes occurring rapidly in the shock waves with both high temporal and spatial resolution.
With our experiment we are venturing into new scientific terrain. We have managed for the first time to use X-ray imaging to quantitatively determine the local properties and the dynamic changes of matter under extreme conditions.
Dr. Andreas Schropp of DESY
The team comprising Prof. Christian Schroer, a DESY physicist, used the Linac Coherent Light Source LCLS at the SLAC National Accelerator Laboratory in the United States to analyze the diamond samples for its pilot work. The researchers hit the narrow edge of a 0.3-mm-thick, 3-cm-longdiamond strip with a brief flash from a high-intensity infrared laser in order to trigger a shock wave. The pulse generated was able to reach a power level of up to 12TW/cm2 and lastfor 150ps. The shock wave generated traversed through the diamond at a speed of 72,000km/h.
“In order to take snapshots of such rapid processes, you need to use extremely short exposure times,” explains Schropp.
The LCLS generated X-ray pulses lasting 50fs, enabling the researchers to film even the quickest movements. However, the researchers needed to repeat the experiment with identical diamond samples for each image due to destruction of the sample after every shot. Therefore, each image was captured at slightly different times. These still images were then assembled to createthe final film,like a “flip book”.
This film enabled the research team to quantitatively measure the density changes in the sample caused by the shock wave. For this purpose, the researchers specially designed an X-ray microscope that allows resolving features of a sample down to 500nm. In conjunction with the speed of sound measured, the researchers were able to determine the state of the diamondunder extreme pressureconditions.
The analysis results revealed that the diamond, known for its hardness, was locally compressed by the powerful shock wave by nearly 10%. This pilot study provides new information about the structure of diamonds.
In view of the remarkable physical properties of diamond it continues to be important both scientifically and technologically. We have for the first time directly imaged shock waves in diamond using X-rays, and this opens up new perspectives on the dynamic behaviour of diamond under high pressure.
Prof. Jerome Hastings of SLAC
The research team believes that it is possible to further improve the spatial resolution to below 100nm by optimising the detector and refining X-ray lasers, for example, for the superconducting X-ray laser currently being constructed at the European XFEL on the DESY campus in Hamburg.
Since X-rays have penetrating power, it possible to apply this technique to almost all solid materials, including aluminium and iron. “The method is important for a series of applications in material science and for describing the physical processes occurring inside planets,” summarises Schroer.
Researchers from the Lawrence Livermore National Laboratory (LLNL) in the United States, the University of Oxford in the UK, and the Technical University of Dresden also contributed to the study.
The study results have been published in the Scientific Reports journal.
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