Plasma decay and energy coupling of femtosecond laser-induced plasma filaments in N2–O2 mixtures

Abstract

In this work, the decay of femtosecond laser-induced plasmas has been explored through both experimental and numerical studies. Understanding the plasma decay in different gas compositions at varying background pressures is crucial in order to establish the capability of localized control of laser energy addition that ultimately can enable various applications. This study investigates the decay dynamics of femtosecond laser-induced plasmas in a varying N2–O2 mixture at varying pressures, with a focus on the role of oxygen in the plasma life and optimization of dual-pulse energy deposition of a second, nanosecond laser pulse. Experimental and simulation analyses show how the presence of oxygen affects the dual-pulse laser plasma decay. Using the self-consistent three-temperature plasma kinetic solver, the key reactions that dominate the temporal behavior of plasma are identified, such as recombination with N4+, electron attachment with O2, associative ionization producing N2+ or NO+, and photo-detachment. The findings are expected to contribute to a deeper understanding of plasma kinetics in both N2-only and N2–O2 environments at various pressures and be of value for advancing the understanding of laser-induced plasmas, optimizing localized energy addition, and advancing low-temperature plasma applications.