Physics

X-ray diffraction enables in-situ ablation depth measurement in aluminum

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When laser energy is applied to a target material, a number of complex processes occur over length and time scales that are too small to be observed visually. To study and ultimately fine-tune such processes, researchers turn to computer modeling. However, these simulations rely on accurate equation of state (EOS) models that describe the thermodynamic properties of the target material (such as pressure, density, and temperature) under the extreme conditions generated by the intense heat of the laser pulse. I’m doing it.

One process that is not adequately addressed in current EOS models is ablation. In ablation, the application of a laser beam removes solid material from a target by evaporation or plasma formation (a fourth state of matter). It is this mechanism that shocks the material, ultimately resulting in the high density required for high-pressure experiments such as inertial confinement fusion (ICF).

To better understand laser-matter interactions related to ablation, researchers at Lawrence Livermore National Laboratory (LLNL), University of California San Diego (UCSD), SLAC National Accelerator Laboratory, and other collaborating institutions are We conducted a study that provides the first example of. Direct time-resolved measurements of ablation depth in aluminum samples using X-ray diffraction. The research is published in Applied Physics Letters.

Controlling the ablation depth of materials is important for a variety of scientific and industrial processes, including laser fusion and astrophysical research, among others. However, measuring ablation depth in the picosecond time domain (trillionths of a second) is a long-standing challenge for laser-induced impact experiments.

This is because previous approaches generally relied on post-irradiation analysis of the target material, making it difficult or impossible to track changes in material response, such as spalls (material deformation effects in response to impact). This is because the influence may cause discrepancies. stress waves) are generated during the experiment.

The study, led by Sophie Parsons, a UCSD graduate student participating in LLNL’s Academic Collaboration Program, involved LLNL scientists Mike Armstrong, Harry Radowski, and John Belloff, who previously worked together during a laser experiment in 2016. The collected X-ray diffraction data were utilized. Her LLNL mentors, Radousky and Armstrong, analyzed this data to extract new information from the aluminum solid phase, but previous analysis explains the point at which the laser shot melted the sample.

The research team mathematically compared the thickness of unshocked aluminum and the amount of ablated aluminum over time, and used in-situ measurements as the shock wave propagated through the target aluminum layer. Obtained. Their in-situ method can focus on laser-matter interactions that occur on picosecond (trillionths of a second) time scales, and is able to focus on the effects that occur during the initial laser-surface interaction. Can be directly measured and separated.

Within the first 10 picoseconds after the laser interacted with the aluminum surface, the researchers observed a rapid decrease in the volume of the solid material.

“This is probably due to the rapid formation of a plasma layer approximately 500 nanometers thick on the laser-irradiated surface, which we call the ‘ablation depth.’ ” said Armstrong, co-author of the paper. The loss of surrounding material then becomes constant over time as the shock wave travels through the remaining unablated aluminum.

Further information: SE Parsons et al, Study of ablation and shock generation across three orders of magnitude of laser intensities with 100 ps laser pulses, Applied Physics Letters (2024). DOI: 10.1063/5.0222979

Provided by Lawrence Livermore National Laboratory

Citation: X-ray diffraction enables in-situ ablation depth measurements in aluminum (November 25, 2024) https://phys.org/news/2024-11-ray-diffraction-enables-situ-ablation Retrieved November 25, 2024 from.html

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