Ionization Dynamics in Intense Laser-Produced Plasmas

TL;DR

This paper investigates the ionization dynamics of laser-irradiated argon plasma, revealing delayed and stepwise ionization processes that challenge traditional models and emphasizing their importance in accurate radiation hydrodynamic simulations.

Contribution

It uncovers the significance of delayed and stepwise ionization processes in laser-produced plasmas, highlighting their impact on ionization states and modeling accuracy.

Findings

Delayed ionization responses are significant.

Stepwise ionization processes influence plasma states.

Low-energy photons can cause ionization.

Abstract

The ionization dynamic of argon plasma irradiated by an intense laser is investigated to understand transient physics in dynamic systems. This study demonstrates that significant delayed ionization responses and stepwise ionization processes are crucial factors in determining the ionization state of such systems. When an intense laser begins to ionize an initially cold argon plasma, the conditions change rapidly, leading to a delayed response in ionization. Consequently, the dynamics do not reach a steady state, even if the electron temperature and density appear unchanged, particularly when the atomic transition process is not sufficiently rapid compared to the relevant time scales. Furthermore, in this case, numerous highly excited states are created primarily through collisional excitation. Thus, even low-energy photons can predominantly ionize plasmas, challenging the conventional belief that such photon energies insufficient to overcome the binding energy of bound electrons typically contribute less to the ionization. These findings underscore the necessity of incorporating these processes in ionization modeling within radiation hydrodynamic simulations for various laser-plasma experiments.