ISSN 1054-660X, Laser Physics, 2012, Vol. 22, No. 12, pp. 1771–1779. © Pleiades Publishing, Ltd., 2012. Original Text © Astro, Ltd., 2012. 1771 1 1. INTRODUCTION Laser produced plasmas play a vital role in many industrial applications such as pulsed laser ablation, trimming of semiconductors, fusion and generation of ion sources. Laser-matter interactions depends upon physical and chemical properties of the material, laser parameters, surrounding ambient conditions and the composition of material used for the pellet formation especially for the analysis of samples in powder forms. Some reports investigated the optimization of the experimental factors by different analytical techniques [1–7]. We used Cr doped in KBr matrix as test element for investigation under different ambient conditions. Laser-induced breakdown spectroscopy (LIBS) is a useful technique for determining the elemental com- position and plasma parameters of various solids, liq- uids and gases [8–22]. The analytical progress of the LIBS technique depends strongly on the best experi- mental conditions. Factors affecting LIBS perfor- mance are mainly, the laser parameters (wavelength, pulse duration, energy, shot to shot power fluctuation and focusing spot size), the ambient conditions (gas, pressure, nature of gas) and the physical properties of the sample, the processes of sample ablation and plasma formation [10–15]. Furthermore, the spectral emission sensitivity of LIBS plasma can be dramati- cally influenced by the surrounding atmospheric pres- sure. The effect of laser irradiance on ablation rate under various Ar, air and He gases were investigated for some metal targets [23–25]. They purposed that the pressure and irradiance are two key factors that can influence the LIBS performance. It is also important 1 The article is published in the original. that such solid pellets must show adequate mechanical strength for LIBS analysis. Hence one has to select carefully a proper binding material to obtain pellets of homogenous shape which can with stand high impact and bear strong mechanical strength [23, 24]. In this work, we present a comparative study to analyze the spectral emission of Cr element doped in KBr matrix under different ambient conditions such as vacuum, air, He and Ar. Our study regarding the effect of ambient conditions on the LIBS signal inten- sity and plasma parameters (T e and n e ) is also impor- tant for the LIBS system to be developed for Mars geology where the ambient pressure is 6 Torr. The study aimed to correlate the surrounding ambient conditions such as gas pressures, nature of gas, plasma parameters at which the most intense spectral emis- sion lines of Cr can be observed. 2. EXPERIMENTAL SETUP A schematic diagram of the LIBS experimental setup used in this work is depicted in Fig. 1. This setup includes a Q-switched Nd:YAG laser source (Spectra- Physics Lasers, Model GCR 100) operating with a maximum peak energy of 100 mJ at 1064 nm having pulse width is 8 ns (FWHM) at repetition rate up to 10 Hz. The laser pulse energy was measured by using a calibrated energy meter (Ophir Model 300). The laser pulses were directed into the cup containing the sam- ple for LIBS signal measurement and the average of ten laser pulses was taken to avoid shot-to-shot varia- tions in the laser plasma. The laser beam was focused using a lens of 30 mm focal length onto the Cr–KBr target kept in the stainless steel vacuum chamber. The matrix material (KBr) was of high purity (99.99%) Effect of Ambient Conditions on Laser-Induced Breakdown Spectra 1 M. A. Gondal a, * and A. A. I. Khalil b, c a Laser Research Group, Physics Department, King Fahd University of Petroleum and Minerals Box 5047, Dhahran 31261, Saudi Arabia b National Institute of Laser Enhanced Sciences, (NILES), Cairo University, Giza 12613, Egypt c Physics Department, Faculty of Science for Girls, Dammam University, Dammam 31113, Saudi Arabia *e-mail: magondal@kfupm.edu.sa Received July 5, 2012 Abstract—The role of different ambient conditions on LIBS signal intensity was investigated for better under- standing and performance of LIBS as a quantitative and qualitative analytical technique. For this purpose, the relative LIBS signal intensities were measured for a standard Cr line (520.8 nm) at different gas pressures of Ar, He, and air. The plasma was generated using a Q-switched pulsed Nd:YAG laser having wavelength of 1064 nm and pulse duration of 8 ns. The analysis revealed that the intensities of the spectral atomic Cr line (520.8 nm) were strongly enhanced under the argon environment in 10–40 mbar range. The electron excitation tempera- ture (T e ) and number density (n e ) were estimated by using a Boltzmann plot and a Stark broadening profile, respectively. For optimum dependence of LIBS, laser energy and pressure dependence was also studied. The electron temperature and number density showed an increase with increase in ambient gas pressure. DOI: 10.1134/S1054660X12120080 LASER SPECTROSCOPY