Influence of pulse-to-pulse delay for 532 nm double-pulse laser-induced breakdown spectroscopy of technical polymers R. Viskup a , B. Praher a , T. Linsmeyer b , H. Scherndl b , J.D. Pedarnig a , J. Heitz a, ⁎ a Christian Doppler Laboratory for Laser-Assisted Diagnostics, Institute of Applied Physics, Johannes Kepler University Linz, A-4040 Linz, Austria b AVE Österreich GmbH, A-4600 Wels, Austria abstract article info Article history: Received 20 April 2010 Accepted 4 September 2010 Available online 15 September 2010 Keywords: Laser induced breakdown spectroscopy (LIBS) Double-pulse laser Polymers Time-resolved plasma plume photography Laser induced breakdown spectroscopy (LIBS) is an emerging technique for fast and accurate compositional analysis of many different materials. We present a systematic study of collinear double-pulse LIBS on different technical polymers such as polyamide, polyvinyl chloride, polyethylene etc. Polymer samples were ablated in air by single-pulse and double-pulse Nd:YAG laser radiation (8 ns pulse duration) and spectra were recorded with an Echelle spectrometer equipped with an ICCD camera. We investigated the evolution of atomic and ionic line emission intensities for different delay times between the laser pulses (from 20 ns to 500 μs) at a laser wavelength of 532 nm. We observed double-pulse LIBS signals that were enhanced as compared to single-pulse measurements depending on the delay time and the type of polymer material investigated. LIBS signals of polymer materials that are enhanced by double-pulse excitation may be useful for monitoring the concentration of heavy metals in polymer materials. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Laser induced breakdown spectroscopy (LIBS) is a versatile method for fast and accurate multi-element analysis of gaseous, liquid and solid samples [1,2]. LIBS provides sensitive and rapid analytical measurement without sample pre-treatment with detec- tion limits in range of ppm. It is also applicable for analysis of powders and inhomogeneous materials [3,4]. In this technique, the material is ablated from the surface of a target by the impact of short and intense laser pulses [5]. The laser irradiation generates a plasma of which the optical emission is collected via a spectrometer and analyzed by a personal computer (PC). The element composition of the target material is obtained from the LIBS spectra by using calibration curves, internal standards or calibration free techniques [6,7]. For polymer and other macromolecular materials, LIBS was mainly employed for detection of additives, especially heavy metals [8,9], and also for classification [10–15]. The double-pulse LIBS approach was proposed for more efficient production of analyte species in excited states. It uses two laser pulses for excitation with a defined delay time between pulses typically in the order of μs. One of the first articles about the double-pulse LIBS configuration for analysis of liquids was published by Cremers at al. in 1984 [16]. Collinear double pulse studies of solid objects in a gas atmosphere were first reported in the mid nineties, see e.g. Ref. [17]. The technique has been re-investigated especially in the last decade for a broad range of materials and for many different measurement parameters (including the use of ultrashort femtosecond or picosec- ond laser pulses) [18–25]. The technique splits into two main streams: (1) collinear double-pulse geometry [26,27], where two laser beams are delivered on the same target surface along the same optical path, and (2) orthogonal geometry [27–32], where only one pulse ablates the sample surface. The double-pulse LIBS approach has received some attention in the scientific community due to the considerable signal enhancement observed for some materials like metals. However, there remains a need for further development and understanding of the underlying physics of double-pulse laser matter interaction, especially in connection with polymers. The main intention of this study is the assessment of the double- pulse LIBS technique for monitoring the concentration of heavy metals in polymer materials. We studied systematically the depen- dence of collinear nanosecond double-pulse LIBS signals on the delay time between the laser pulses for different technical polymers, for certified reference polymers, and for polymer waste materials with heavy metals additives. Special attention was given to interpulse- delay times between 20 ns and 10 μs. LIBS spectra were recorded in air and plasma characterization was performed by time-resolved plume photography. 2. Experimental 2.1. Instrumentation The experimental setup for double-pulse laser induced plasma spectroscopy and time resolved plasma plume photography is Spectrochimica Acta Part B 65 (2010) 935–942 ⁎ Corresponding author. E-mail address: johannes.heitz@jku.at (J. Heitz). URL: http://www.cdlabor-lad.jku.at/ (J. Heitz). 0584-8547/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2010.09.003 Contents lists available at ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab