Article A Simple Device for Lens-to-Sample Distance Adjustment in Laser-Induced Breakdown Spectroscopy (LIBS) Juliana Cortez 1 , Benedito B. Farias Filho 1 , Laiane M. Fontes 1 , Celio Pasquini 1 , Ivo M. Raimundo Jr 1 , Maria Fernanda Pimentel 2 , and Fla ´via de Souza Lins Borba 3 Abstract A simple device based on two commercial laser pointers is described to assist in the analysis of samples that present uneven surfaces and/or irregular shapes using laser-induced breakdown spectroscopy (LIBS). The device allows for easy positioning of the sample surface at a reproducible distance from the focusing lens that conveys the laser pulse to generate the micro-plasma in a LIBS system, with reproducibility better than 0.2 mm. In this way, fluctuations in the fluence (J cm –2 ) are minimized and the LIBS analytical signals can be obtained with a better precision even when samples with irregular surfaces are probed. Keywords Laser-induced breakdown spectroscopy, LIBS, lens-to-sample distance, sample positioning, repeatability Date received: 16 May 2016; accepted: 6 December 2016 Introduction Laser-induced breakdown spectroscopy (LIBS) has gained growing interest as a technique capable of analyzing samples in any physical state, in a quasi nondestructive way, with microanalysis capability, showing the possibility to operate in the field using portable instruments and to perform stand-off analyses. 1–8 In brief, the technique employs a laser to produce a short duration radiation pulse (fs to ns, 2–300 mJ pulse –1 ), which is focused by a lens on the surface of a solid sample. The fluence (energy density, J m –2 ) reaches high enough values at the small illuminated area by the focused beam to ablate a tiny amount of the material, producing a high temperature micro-plasma and exciting the atomized and ionized species found in the plasma. The emitted radia- tion is typically analyzed by monochromators such as those based on echelle optics and directed to a two-dimensional detector array. With laser pulses of nanoseconds (ns), the detection system is usually gated and synchronized with pulse triggering, allowing for definition of a time interval (on the order of a few ms) to delay the detection of the emitted radiation until the intense continuum radiation background fades, and an integration time interval (also in the order of a few ms) during which the emitted radiation is measured. The detector array signal is treated to generate an emission spectrum that contains qualitative and quanti- tative information about the chemical composition of the sample. The energy density or fluence is one of the most rele- vant parameters in controlling the repeatability of the whole process of obtaining a LIBS signal. Among others, this parameter is related to the amount of ablated material, the electron number density and the temperature of the micro-plasma. 2–4 Of course, any variation in this parameter causes significant changes in the LIBS spectrum, mainly in the intensities of the atomic/ionic emission lines of the elements present in the sample. 1 Chemistry Institute, Department of Analytical Chemistry, UNICAMP, Campinas, SP, Brazil 2 Department of Chemical Engineering, Federal University of Pernambuco, Recife, PE, Brazil 3 Department of Fundamental Chemistry, Federal University of Pernambuco, Recife, PE, Brazil Corresponding author: Ivo M. Raimundo Jr., Chemistry Institute, CP 6154 Campinas, 13083-970 Brazil. Email: ivo@iqm.unicamp.br Applied Spectroscopy 0(0) 1–6 ! The Author(s) 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0003702816687571 journals.sagepub.com/home/asp