By combining experimental measurements and modeling, scientists have precisely described the process of interaction between a femtosecond laser and amorphous silica.
The modeling of this complex, multiphysics, and multiscale phenomenon, experimentally validated, can now be used to control laser/matter interaction, with the aim of optimizing material processing or functionalizing them via 3D structuring. These results are published in the journal
Physical Review B.
Femtosecond pulse lasers allow for the creation of a strong, localized interaction between light and matter. It is a complex, multiphysics and multiscale process because various physical processes occur over an extended time scale, from hundreds of femtoseconds (10
-15s) to nanoseconds (10
-9s). Better understanding this phenomenon could improve numerous material processing and structuring techniques using femtosecond lasers, some of which are already used industrially.
A team from the Lasers, Plasmas and Photonic Processes Laboratory (
LP3, Aix-Marseille University/CNRS) developed an experimental setup designed to gather quantitative data on the interaction of a femtosecond laser with glass (amorphous silica), across all time scales of the phenomenon.
Two laser beams are used: one to create the interaction with the material, the other to make optical measurements. The transmission measurements reveal the amount of laser energy absorbed by the matter, while birefringence measurements— a property characterizing the material's anisotropy— help to evaluate the stresses created by the intense local pressures induced.
An ultrashort laser pulse is focused inside a glass (SiO2) (top image). It induces material photoionization, as revealed by transient optical transmission measurements (lower left). The relaxation of energy is partially carried out by the emission of a shockwave, highlighted by transient birefringence measurements (lower right).
© LP3 (CNRS/AMU)
A multiphysics model of laser/matter interaction was developed, taking into account the propagation of laser pulses, the dynamics of the electrons created by the material's photoionization, and the material's response to the energy it receives. Simulations carried out with this model, which has been experimentally validated, have allowed the prediction of the temporal evolution of the material's local properties during the interaction process.
The researchers were able to evaluate the maximum local pressure generated by the intense and ultrashort laser pulse (>10 GPa), as well as the temperature reached (>10,000 K). Furthermore, the study also revealed that, contrary to popular belief, only a low-amplitude, short-lived shockwave (<500 ps) is generated by the interaction with the laser. A minimal fraction of the absorbed laser energy (2%) contributes to generating this wave.
Having a validated model covering the entire interaction process should now make it possible to better control laser/matter interaction, for example, to achieve desired structuring or to avoid defect appearance during material laser processing (cutting, marking, welding, etc.). The LP3 team has thus launched a new project funded by ANR,
Espresso, aimed at exploring the potential for functionalizing silica by locally modifying its optical, mechanical, and thermal properties.
References:
Quantitative assessment of femtosecond laser-induced stress waves in fused silica.
Olga Koritsoglou, Guillaume Duchateau, Olivier Utéza, and Alexandros Mouskeftaras.
Physical Review B, published on August 26, 2024.
https://doi.org/10.1103/PhysRevB.110.054112
Article available on the open archives platform
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