Numerical investigation of nanosecond laser induced plasma and shock wave dynamics from air using 2D hydrodynamic code

Abstract

A two-dimensional axis symmetric hydrodynamic model was developed to investigate nanosecond laser induced plasma and shock wave dynamics in ambient air over the input laser energies of 50–150 mJ and time scales from 25 ns to 8 μs. The formation of localized hot spots during laser energy deposition, asymmetric spatio-temporal evolution, rolling, and splitting of the plasma observed in the simulations were in good agreement with the experimental results. The formed plasma was observed to have two regions: the hot plasma core and the plasma outer region. The asymmetric expansion was due to the variation in the thermodynamic variables along the laser propagation and radial directions. The rolling of the plasma was observed to take place in the core region where very high temperatures exist. Similarly, the splitting of the plasma was observed to take place in the core region between the localized hot spots that causes the hydrodynamic instabilities. The rolling and splitting times were observed to vary with the input laser energy deposited. The plasma expansion was observed to be asymmetric for all the simulated time scales considered, whereas the shock wave evolution was observed to transfer from asymmetric to symmetric expansion. Finally, the simulated temporal evolution of the electron number density, temperature of the hot core plasma, and the temperature evolution across the shock front after the detachment from the plasma were presented over the time scales 25 ns–8 μs for different input laser pulse energies.