Key words: supercritical water, molecular dynamics, interaction of laser radiation with matter
The dynamics of femtosecond laser action on water was experimentally studied and reconstructed using numerical modeling based on the classical molecular dynamics method in combination with a two-temperature model and dynamic rate equations. This process occurs in several stages: initially, a femtosecond laser pulse interacts with the electron subsystem, generating plasma due to multi photon, tunnel and impact ionization. The energy transfer from plasma electrons to atoms, as shown using the two-temperature model, leads to ultra-fast heating of the substance to a temperature about 10,000 K, and the pressures achieved in the area of action are about 15 GPa, which leads to the generation of a shock wave. The excess of temperatures and pressures over critical values in combination with high density fluctuations and clustering allow us to assert the transition of the substance to a supercritical state. Pressures and temperatures exceeding critical values are achieved in a region slightly exceeding the cavitation region, and this region experiences oscillations with a period close to the period of oscillations of the cavitation bubble. It is shown that in the case of femtosecond laser action, the specific energy input measured experimentally can be immediately used as initial conditions, assuming instantaneous heating of the medium, which significantly simplifies numerical modeling. Within the framework of this approach, both the pressures achieved at the shock wave front and the dynamics of cavitation bubbles are successfully reconstructed.
doi:10.1134/S1990793124030011