Influence of surrounding gas, composition and pressure on plasma plume dynamics of nanosecond pulsed laser-induced aluminum plasmas

Mahmoud S Dawood,Joëlle Margot,Ahmad Hamdan

doi:10.1063/1.4935100

Abstract

In this article, we present a comprehensive study of the plume dynamics of plasmas generated by laser ablation of an aluminum target. The effect of both ambient gas composition (helium, nitrogen or argon) and pressure (from ∼5 × 10−7 Torr up to atmosphere) is studied. The time- and space- resolved observation of the plasma plume are performed from spectrally integrated images using an intensified Charge Coupled Device (iCCD) camera. The iCCD images show that the ambient gas does not significantly influence the plume as long as the gas pressure is lower than 20 Torr and the time delay below 300 ns. However, for pressures higher than 20 Torr, the effect of the ambient gas becomes important, the shortest plasma plume length being observed when the gas mass species is highest. On the other hand, space- and time- resolved emission spectroscopy of aluminum ions at λ = 281.6 nm are used to determine the Time-Of-Flight (TOF) profiles. The effect of the ambient gas on the TOF profiles and therefore on the propagation velocity of Al ions is discussed. A correlation between the plasma plume expansion velocity deduced from the iCCD images and that estimated from the TOF profiles is presented. The observed differences are attributed mainly to the different physical mechanisms governing the two diagnostic techniques.

Highlights

The interaction of high-energy pulsed laser beams with matter is a field of greater and greater importance since the discovery of lasers
A correlation between the plasma plume expansion velocity deduced from the intensified Charge Coupled Device (iCCD) images and that estimated from the TOF profiles is presented
The interaction of the laser beam with the evaporating material leads to the formation of isothermally expanding plasma until the end of the laser pulse (∼10 ns in our case)

Summary

Introduction

The interaction of high-energy pulsed laser beams with matter is a field of greater and greater importance since the discovery of lasers. In the case of gas medium, techniques are being developed to determine the elemental composition of trace elements present in the medium.[1] focusing of a laser beam in a gas leads to the formation of an energetic shock wave which can be used in propulsion systems.[2] When the medium is liquid, the plasma is usually used for elemental characterization of the liquid (e.g. water).[3] in most laser-based techniques, the laser is focused on the surface of a solid material (target). The ablated species are highly confined to a small region in the vicinity of the solid-liquid interface due to the inertia of the liquid.[10,11] This region can show a high density of energetic species together with high pressure and high temperature, which forms a suitable medium for the growth of some crystallographic phases.[12]

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