Optimally enhanced optical emission in laser-induced breakdown spectroscopy by combining spatial confinement and dual-pulse irradiation

L B Guo,Y S Zhou,T Wu,J B Park,C M Li,X N He,B Y Zhang,Y F Lu,X Y Zeng

doi:10.1364/oe.20.001436

Abstract

In laser-induced breakdown spectroscopy (LIBS), a pair of aluminum-plate walls were used to spatially confine the plasmas produced in air by a first laser pulse (KrF excimer laser) from chromium (Cr) targets with a second laser pulse (Nd:YAG laser at 532 nm, 360 mJ/pulse) introduced parallel to the sample surface to re-excite the plasmas. Optical emission enhancement was achieved by combing the spatial confinement and dual-pulse LIBS (DP-LIBS), and then optimized by adjusting the distance between the two walls and the interpulse delay time between both laser pulses. A significant enhancement factor of 168.6 for the emission intensity of the Cr lines was obtained at an excimer laser fluence of 5.6 J/cm(2) using the combined spatial confinement and DP-LIBS, as compared with an enhancement factor of 106.1 was obtained with DP-LIBS only. The enhancement mechanisms based on shock wave theory and reheating in DP-LIBS are discussed.

Highlights

Over the last few decades, laser-induced breakdown spectroscopy (LIBS) has been demonstrated as a promising and useful element analysis technique [1–8]
spatially confine the plasmas produced in air by a first laser pulse
Optical emission enhancement was achieved by combing the spatial confinement and dual-pulse LIBS

Summary

Introduction

Over the last few decades, laser-induced breakdown spectroscopy (LIBS) has been demonstrated as a promising and useful element analysis technique [1–8]. LIBS offers a simple and fast method of elemental analysis. The ability to form a plasma on unprocessed samples makes LIBS an amazingly versatile diagnostic tool [9–11]. It is one of the few techniques that can be used for non-contact elemental analysis, making LIBS uniquely suited to measurements of hazardous materials and materials in difficult-to-reach locations [12,13]. Continuous studies have been made to improve the sensitivity of LIBS. These studies have led to investigations such as dual-pulse excitation and various plasma confinements [18–25]

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