Spatial, temporal, and spectral characterization and kinetic investigations of a high repetition-rate laser-induced micro-plasma in air

Abstract

Advances in laser-induced plasmas have enabled various rapid and simple analytical applications. Especially, their uses in the analyses of condensed-phase samples have drawn significant attention in the past few decades. Depending on the laser energy per pulse, various analytical goals can be achieved. Laser-induced airborne plasmas allow direct analysis of species in ambient air. Importantly, all of these applications are based on a fundamental understanding of the laser–medium interaction. Recent developments of diode-pumped solid-state lasers offer an alternative to conventional powerful, yet bulky lasers, which can specifically operate at high repetition rates. Although these lasers deliver much lower power per pulse (μJ compared to mJ), the outstanding repetition rates offer significant improvement to meet statistical needs in some cases. In the present work, a μJ-laser-induced airborne plasma was characterized through optical emission analysis. By using a ns-time-gated image detector coupled with specific bandpass filters, spatially, temporally, and spectrally resolved plasma images were recorded. Compared to conventional mJ-laser-induced plasmas, the one induced by μJ-lasers demonstrated unique features during its evolution. Specifically, measurements of the distribution of ionic and atomic species revealed distinctive energy/matter transfer processes during early ignition of the plasma. Meanwhile, dynamic investigations suggested subsequent matter transport in the later stage.