Particle-In-Cell simulation of silicon laser ablation and formation of over-dense plasma*

The efficient coupling of laser energy to a solid target is of the great importance in many research areas related to laser-matter interactions. The laser light doesn’t penetrate deeply into a preformed over-dense plasma. The energy is deposited into the deeper solid layers by the hot electrons with energies of tens of keV. The ablation of silicon and expansion of plasma generated by a short laser pulse with intensity of 10¹⁵ W/cm² are studied using the Smilei Particle-In-Cell (PIC) code. The collisions between macro-particles and ionization are taken into account. The kinetic PIC simulation allows to investigate how the material is removed when the electron density is above the critical density of plasma. The over-dense plasma was found to be characterized by very steep profiles of electron density and temperature. The PIC results provide insights into the time evolution of 1) number density of ions and electrons along the depth of plasma layer; 2) electric and magnetic fields; 3) total ion, electron, and electromagnetic field energies; and 4) energy spectra of ions and electrons.