Correlation of acoustic and optical emission signals produced at 1064 and 532 nm laser-induced breakdown spectroscopy (LIBS) of glazed wall tiles ☆ Aleš Hrdlička a, ⁎, Linda Zaorálková a , Michaela Galiová a , Tereza Čtvrtníčková a , Viktor Kanický a , Vítězslav Otruba a , Karel Novotný a , Pavel Krásenský a , Jozef Kaiser b , Radomír Malina b , Kateřina Páleníková b a Dep. of Physical Electronics, Dep. of Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 BRNO Czech Republic b Institute of Physical Engineering, Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, 616 69 BRNO Czech Republic abstract article info Article history: Received 30 October 2007 Accepted 24 October 2008 Available online 12 November 2008 Keywords: LIBS Acoustic signal Normalization Internal standard Ceramic tile Depth profiling An acoustic signal was used for the internal standardization of laser-induced breakdown spectroscopy (LIBS) of a glazed wall tile. For the LIBS analyses, 1064 nm and 532 nm wavelengths of the Nd:YAG laser were utilized. The tile was depth profiled by a single-spot ablation from the glaze into the substrate. Some lines of major elements Si(I) 252.418, Si(I) 252.851, Al(I) 257.509, Cr(I) 295.368, Al(I) 309.271 nm and Ti(II) 334.904 nm were monitored. The decrease in the optical emissions during the ablation was successfully compensated for by normalization to the square power of the acoustic signal in the interval of 290–340 nm. This approach failed for the lines between 250–270 nm. The results were the same for both lasing wavelengths despite different irradiances. The acquired profiles are in good agreement with the reference X-ray fluorescence measurement. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The feasibility of LIBS quantification depends upon many para- meters [1–5]. It has been well-known for a long time that laser ablation (LA), i.e. the interaction between a laser beam and an analytic material, is a very complex process which is difficult to describe generally. Except for a standard reference material, which has a structure as similar as possible to the analytical sample [1], an internal standardization is often required [3–5]. Among others, an acoustic signal has been used for this purpose [6,7]. During the LA process this signal is always generated. Part of the pulse energy is transformed into a so-called acoustic shockwave [7–16]. The parameters of the shockwave are very variable and do not only depend on the LA pulse (Pulse parameters e.g. energy, focus point etc. can be adjusted), but are mainly dependent on the ablated material. Consequently, the simultaneous monitoring of the acoustic emission may be advanta- geous for inhomogeneous samples or for a depthwise analysis of sandwich structures [10,11] as well as for laser cleaning [12,13]. The propagation velocity of the wave can be used for an on-line determination of the drilled crater depth. Nevertheless, this approach is limited by the velocity and precision of affordable electronics based on well-known physical principles [16]. Indeed it is more suitable for industrial purposes such as laser micromachining. Success of the acoustic standardization lies in a good correlation between the ablated mass, optical emission of particular lines and the portion of the beam shot energy that is transformed into a detectable acoustic wave [8,11,15,17]. The relationship between the acoustic signal and the fluence depends on several parameters. They are mainly: surface response, bulk and morphology response after various numbers of pulses [18]. Thus, the acoustic emission of the sample itself may not represent the ablation process sufficiently and some additional characteristics of the microplasma must be determined such as electron density, excitation or electron temperature [1–3, 7]. The accompanying acoustic signal changes not only its intensity but also its frequency spectrum depending on the ablation conditions employed [14,15]. However, once a piece of solid material is fixed to an ablation stage, the acoustic frequency response of the system remains unchanged during the ablation process. The conversion of the laser beam energy into an acoustic shockwave has already been investi- gated [8]. It depends on many factors and the shockwave just around the ablation spot shows a complicated structure [9]. The acoustic signal is also applicable in the field of soft laser desorption techniques (MALDI) [19,20] and may be of benefit to laser ablation-inductively coupled plasma-optical emission spectroscopy (LA-ICP-OES) [21,22]. This paper discusses the feasibility of using the acoustic emission resulting from the interaction on glazed ceramic wall tiles for the sake of internal standardization. To this purpose, the behavior of several spectral lines of major elements has been investigated. The applic- ability of both the fundamental 1064 nm and the second harmonic 532 nm Nd:YAG laser wavelengths was tested because they are easy Spectrochimica Acta Part B 64 (2009) 74–78 ☆ This paper was presented at the Euro Mediterranean Symposium on Laser Induced Breakdown Spectroscopy (EMSLIBS 2007) held in Paris (France), 11–13 September 2007. ⁎ Corresponding author. Tel.: +420 54949 4285; fax: +420 54949 2494. E-mail address: ales2003h@centrum.cz (A. Hrdlička). 0584-8547/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2008.10.043 Contents lists available at ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab