1674 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 42, NO. 6, JUNE 2014 Spectroscopic Evolution of Plasma Produced by Nd-YAG Laser H. Hegazy, E. AlAshkar, H. H. Abou-Gabal, M. Naguib Aly, and N. Hamed Abstract—The aim of this paper is to evaluate the effect of the laser beam energy on the properties of the plasma generated by focusing an intense laser beam on Zn solid targets in air at atmospheric pressure. Plasma is generated using Nd-YAG pulsed laser from Quanta at the fundamental and visible wavelength, its duration being 6 ns. This paper has been done at laser energies of 350, 200, and 100 mJ for the fundamental wavelength, and of 400, 200, and 100 mJ for the second-harmonic laser. The emitted light is collected by a fiber cable and illuminates the entrance slit of an Acton grating spectrometer equipped with intensified charge coupled device camera from photoionization at several delay time intervals. Boltzmann plots of Fe I spectral lines are used to obtain the excitation temperature evolution of the produced plasmas. The evolution of the plasma density is obtained from the Stark full-width at half-maximum of the Si I line at 288.16 nm and Al II line at 281.6 nm. In this paper, we are able to perform experiments at different laser energies and different delay times, which also allow us to study the dependence of the plasma evolution on the laser wavelength. Index Terms— Laser-plasma interactions, laser-plasma interac- tions with solids targets, laser-produced plasma, optical emission spectroscopy (OES), plasma diagnostics. I. I NTRODUCTION L ASER-INDUCED plasmas (LIPs) advance and progress as they represent an important plasma technique: fundamental aspects of laser-solid interaction and consequent plasma generation, applied techniques in material processing technology, and sample elemental analysis are involved [1], [2]. The interaction of laser light with solid targets is a complicated process and it is not completely understood. It consists of different stages: 1) the laser ablation of the target; 2) plasma generation; 3) laser interaction with the plasma; and 4) plasma expansion and collision with target material [3]. However, the interaction of laser light with the solid targets and the consequent produced plasma are being studied by a growing number of research groups [4]–[12]. Manuscript received December 1, 2013; revised March 4, 2014; accepted April 9, 2014. Date of publication May 19, 2014; date of current version June 6, 2014. H. Hegazy is with the Department of Physics, Faculty of Science, Jazan University, Jazan 2097, Saudi Arabia, and also with the Department of Plasma Physics, Nuclear Research Centre, Egyptian Atomic Energy Authority, Enshass 13759, Egypt (e-mail: hossamhegazy@jazanu.edu.sa). E. AlAshkar is with the Physics Division, National Research Centre, Depart- ment of Spectroscopy, Dokki 12511, Egypt (e-mail: eaashkar@yahoo.com). H. H. Abou-Gabal, M. Naguib Aly, and N. Hamed are with the Department of Nuclear and Radiation Engineering, Faculty of Engineering, Alexandria University, Alexandria 21544, Egypt (e-mail: hanaaag@hotmail.com; naguib- halyx@yahoo.com; nesmanuclear_95@yahoo.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPS.2014.2318016 In particular, plasmas evaporated by irradiating solid targets with visible and ultraviolet nanosecond laser pulses at moder- ate energy density are widely used for the deposition of thin solid films, where the technique has been applied successfully to a wide range of materials, including metals, semiconductors, insulators, and superconductors [13], [14]. Moreover, nanopar- ticles are of great interest for many technological applications and are subject of fundamental research due to their size dependent physical properties [15]. The most known set of investigation techniques dealing with LIPs includes optical emission and absorption spectrom- etry, mass spectrometry, time-of-flight, and charge collection measurements [3], [13]. The optical emission spectroscopy (OES) of LIPs, which has been called laser-induced plasma spectroscopy (LIPS) or laser-induced breakdown spectroscopy (LIBS), has become a powerful tool for the fundamental studies of the interaction of laser beams with materials [16]. As an analytical technique, LIBS has demonstrated its unique versatility, allowing fast contact-less analysis of almost any type of material and the possibility to adapt the technique to the special requirements of diverse practical analytical problems. One of the distinguishing features of LIBS is its capability to carry out the characterization of the LIP. The spectroscopy of the radiation emitted by LIPs may be used to obtain characteristic physical parameters, such as the tem- perature, electron number density, and atom and ion number densities. As the spectral line and continuum emission of the plasmas depend in turn on these parameters, the interest of plasma characterization in order to achieve improvements in the applications of LIBS is clear [17]. Adrain and Watson [18] described the principles for char- acterization of LIPs by OES, where some experimental stud- ies and the instrumentation required were also reported. Cremers and Radziemski [19] described the early works on laser plasma characterization and analytical applications. Radziemski and Cremers [20] discussed the laser-induced plasmas (LIPs) and their applications, which included the principles of laser plasma spectroscopy used for characteriza- tion and spectrochemical analysis. Geohegan [21] described the diagnostics techniques used for characterization of the pulsed laser deposition plasma plumes, including OES tech- niques. Miziolek et al. [22] and Cremers and Radziemski [23] described principles, techniques, and experiments related to LIP characterization. Pasquini et al. [24] discussed the subject of LIPs with a general description of the instrumentation used in LIBS. In the two decades following the invention of the laser in 1960, the characterization of LIP was a subject of intense 0093-3813 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.