Laser-driven shock wave dynamics in aluminum target

This study investigates the dynamics of plasma and shock wave generated during nanosecond laser ablation of the aluminum target over a broad range of laser fluence (15-700 J/cm2). The optical probe beam deflection apparatus coupled with laser-induced breakdown spectroscopy is applied to track and elucidate the evolution of laser-induced plasma and shock waves. Our findings reveal a rapid increase in shock wave velocity and pressure with increasing fluence, reaching a maximum of 4 km/s and 100 MPa at 350 J/cm2, followed by saturation at higher fluences. These findings align well with the CJ detonation velocity model and Fabbero's model for laser ablation dynamics. The study also highlights the rapid decay of shock wave's velocity and pressure in the near-field region, adhering to the Sadowski and blast wave model and approaching typical acoustic waves within a few mm of the target surface. Plasma temperature and electron density peaked at 350 J/cm2, confirming the effect of the reflection of the trailing laser pulse by the induced plasma. Our study revealed a direct relationship between SW pressure and ablated mass, resulting in a constant mass-specific shock wave pressure that increases linearly with laser fluence and remains constant beyond 350 J/cm2. The laser-induced breakdown spectroscopy analysis also uncovered a significant decrease in the electron number density and plasma temperature with time, following a power-law relationship. These insights enhance understanding of the underlying physics of laser-induced shock wave, paving the way for material processing and micromachining applications.