Mimicking the earth core conditions with ultrafast laser materials interaction

Ultrafast lasers create extreme, non-equilibrium thermodynamic conditions that can transiently reach pressures and temperatures comparable to interior core of the earth. Here we show that femtosecond excitation of amorphous silica-hafnia multilayer dielectrics drives the formation of high-pressure crystalline phases of silica including stishovite, seifertite, and the pyrite-type high density structure, within confined subsurface regions.Using TEM, SAED, and 4D-STEM, we directly map nanoscale phase evolution and identify crystalline motifs embedded inside laser generated blisters.Complementary molecular dynamics simualtions reveal the thermodynamic pathway underlying these transformations, where rapid electronic pressure initiates densification and octahedral coordination, followed by temperature driven crystallization and displacive transitions during ultrafast quenching. The resulting polymorphs reflects a dual-stage pathway inaccessible under equilibrium processing. Our results establish femtosecond laser excitation as a viable route to synthesize and stabilize ultrahigh-density high pressure silica phases under ambient conditions, without a diamond anvil cell, with implications for laser-damage mechanisms, high-energy-density materials, and planetary physics.

💡 Research Summary

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This paper demonstrates that femtosecond laser pulses can transiently generate thermodynamic conditions comparable to those found in the Earth’s core—pressures of 100–300 GPa and temperatures exceeding 4000 K—within nanometer‑scale volumes of a SiO₂/HfO₂ multilayer dielectric stack. By delivering single‑shot laser pulses of 25 fs, 77 fs, and 260 fs duration at 1030 nm wavelength, the authors induce well‑defined subsurface blisters in the upper silica layers. Cross‑sectional lamellae prepared by focused ion beam (FIB) are examined with bright‑field and high‑resolution transmission electron microscopy (TEM), selected‑area electron diffraction (SAED), and four‑dimensional scanning transmission electron microscopy (4D‑STEM).

Electron diffraction reveals the coexistence of several high‑pressure silica polymorphs inside the blister cavity: the octahedrally coordinated stishovite phase, its denser derivative seifertite, and a pyrite‑type structure characterized by a 6 + 2 silicon coordination. 4D‑STEM mapping shows that these crystalline domains are concentrated near the blister centre, where the transient pressure is highest, and gradually transition to amorphous SiO₂ toward the periphery.

To elucidate the underlying physics, the authors perform non‑equilibrium molecular dynamics (MD) simulations that explicitly model the rapid generation of a dense electron–hole plasma, the ensuing electronic pressure surge, and the subsequent electron‑phonon coupling that heats the lattice. Unlike earlier works that relied on the Berendsen thermostat, the present simulations employ proper NVT/NVE ensembles, allowing realistic temperature fluctuations and nucleation events. The MD results indicate a two‑stage pathway: (1) an ultrafast electronic pressure pulse compresses the silica network, forcing a rapid transition from tetrahedral to octahedral Si coordination; (2) lattice heating melts the compressed material, and an almost instantaneous quench (tens of picoseconds) freezes the high‑density configurations, producing metastable high‑pressure phases.

Density functional theory (DFT) calculations of Gibbs free energies for the identified phases confirm that, under the simulated non‑ambient conditions, the pyrite‑type structure possesses the lowest free energy, explaining its persistence after the laser pulse. The authors also discuss how the HfO₂ layers act as a confinement medium, enhancing plasma density and limiting heat diffusion, thereby localizing the extreme pressure‑temperature state.

The work reframes femtosecond‑laser‑induced damage in silica not merely as mechanical failure but as a chemically driven phase transformation. The formation of high‑pressure polymorphs creates residual internal stresses that lower the laser‑induced damage threshold, offering a new perspective for designing more resilient optical components. Moreover, the ability to synthesize and stabilize ultra‑dense silica phases without a diamond anvil cell opens avenues for high‑energy‑density material research, planetary interior modeling, and the exploration of other systems (e.g., Fe, Mg, Fe‑O, carbon) embedded in similar multilayer stacks.

Limitations include the reliance on post‑mortem microscopy, which precludes direct observation of the ultrafast transformation dynamics, and the lack of in‑situ pressure/temperature diagnostics within the blister. Future studies are suggested to employ femtosecond X‑ray diffraction or ultrafast electron diffraction to capture real‑time structural evolution, and to explore a broader range of multilayer compositions to map the pressure‑temperature phase space more comprehensively.

In summary, this study provides the first experimental verification that femtosecond laser excitation can create Earth‑core‑like extreme conditions in a solid dielectric, drive silica along a non‑equilibrium thermodynamic pathway, and stabilize high‑pressure silica polymorphs at ambient pressure. This breakthrough establishes a versatile, tabletop platform for high‑pressure material synthesis and offers new insights into laser‑damage mechanisms, with significant implications for optics, materials science, and planetary physics.