Enhancement of optical emission from laser-induced plasmas by combined spatial and magnetic confinement

L.B Guo,Z.X Cai,Y.F Lu,W Hu,Y.S Zhou,B.Y Zhang,C.M Li,X.N He,X.Y Zeng

doi:10.1364/oe.19.014067

Abstract

To enhance optical emission in laser-induced breakdown spectroscopy, both a pair of permanent magnets and an aluminum hemispherical cavity (diameter: 11.1 mm) were used simultaneously to magnetically and spatially confine plasmas produced by a KrF excimer laser in air from pure metal and alloyed samples. High enhancement factors of about 22 and 24 in the emission intensity of Co and Cr lines were acquired at a laser fluence of 6.2 J/cm2 using the combined confinement, while enhancement factors of only about 11 and 12 were obtained just with a cavity. The mechanism of enhanced optical emission by combined confinement, including shock wave in the presence of a magnetic field, is discussed. The Si plasmas, however, were not influenced by the presence of magnets as Si is hard to ablate and ionize and hence has less free electrons and positive ions. Images of the laser-induced Cr and Si plasmas show the difference between pure metallic and semiconductor materials in the presence of both a cavity and magnets.

Highlights

Within the past decades, laser-induced breakdown spectroscopy (LIBS) has become a wellestablished and powerful optical emission spectroscopy (OES) analytical technique [1,2,3,4,5]
To enhance optical emission in laser-induced breakdown spectroscopy, both a pair of permanent magnets and an aluminum hemispherical cavity were used simultaneously to magnetically and spatially confine plasmas produced by a KrF excimer laser in air from pure metal and alloyed samples
High enhancement factors of about 22 and 24 in the emission intensity of Co and Cr lines were acquired at a laser fluence of 6.2 J/cm2 using the combined confinement, while enhancement factors of only about 11 and 12 were obtained just with a cavity

Summary

Introduction

Laser-induced breakdown spectroscopy (LIBS) has become a wellestablished and powerful optical emission spectroscopy (OES) analytical technique [1,2,3,4,5]. The plasma is confined by the magnetic field; on the other hand, the shock wave spreads out at a very high speed, and will be reflected back when encountering walls and will compress the plasma [20]. Combining these two effects, the plasma is compressed into the center, resulting in highly increased collision rates among particles within the plasma which leads to an increase in the number of atoms in high-energy states and, enhanced emission spectra intensity [21, 22]. The OES and fast imaging of the plasma plumes were investigated to study the evolution of the plasmas

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