Femtosecond laser; Laser-induced breakdown spectroscopy; Nanoparticle; Double pulse;FIELD ENHANCEMENT; METALLIC SAMPLES; PLASMA; LIBS; CONFINEMENT; IMPROVEMENT; DISCHARGE; ABLATION; SURFACE; ARRAYS

Metal nanoparticle deposition on sample surface is a promising approach to enhance the emission signal during laser-induced breakdown spectroscopy(LIBS). In this article, strong optical emission enhancement was achieved by combining nanoparticle enhanced LIBS (NELIBS) and double pulse LIBS (DP-LIBS) on a crystal SiO2 sample by using femtosecond laser. Thermal dewetting was used to deposit gold (Au) nanoparticles (NPs) on sample surface and NPs with different size were obtained by altering the thickness of the Au film. It was found that both the size and distribution of Au NPs significantly affected the enhancement effect of NELIBS and the Au NPs made from 7.5 nm gold film had the best enhancement effect. The fundamental features of NELIBS enhancement for dielectric target were investigated by studying the photon absorption process. At a low laser fluence of 4.4 J/cm(2), an enhancement factor of about 13 for spectrum intensity was obtained in NELIBS and reached to 30 after being combined with DP-LIBS. (C) 2017 Elsevier Ltd. All rights reserved.