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.

In this study, a new approach for Laser-induced Breakdown Spectroscopy (LIBS) with gold nanofilm (NF) deposited on sample surface was carried out by using femtosecond laser. Different materials including metallic sample, semiconductor sample and dielectric sample were tested. Strong emission enhancement was obtained on SiO2, ceramic and Si sample. It was found that different lines in ceramic sample had different enhancement effect, which was probably related to concentration of different substances in ceramic. The enhancement effect was found to weaken with the increase of laser fluence. Enhancement factors of about 14 for SiO2, 5 for ceramic and 3 for Si sample were achieved at laser fluence of 3.3 J/cm(2), which decreased to 9 for SiO2, 3 for ceramic and 1.5 for Si sample at laser fluence of 8.8 J/cm(2). The mechanism of nanofilm-enhanced LIBS (NFELIBS) was localized surface plasmon resonance, which could change the dominant photon ionization process of sample.