الفهرس 
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Abstract
Laser induced break down spectroscopy (LIBS) or laser induced plasma spectroscopy (LIPS) was intensively studied in the last decade as a new analytical technique. This technique deals with the study of the spectral distribution of line intensities and the line shapes, of the optical emission and allow for an acceptable spatial & temporal resolution of the detected spectra. It is increasingly seen as a viable analytical technique. It is a promising tool for the analysis of trace impurities in metals. In LIBS technique, a powerful laser pulse is focused on a surface, a tiny amount of material is vaporized and through further photon absorption, it is heated up until it ionize and expand from the sample surface as a plasma cloud. This laser – induced plasma is a micro – source of light that can be analyzed spectrally and temporally resolved detection of characteristic emission by a spectrometer. This is the principle of laser – induced plasma spectroscopy (LIBS). The ability to determine the composition of a metal surface under water is a milestone and has several applications. Examples include in situ detection of archeological objects sank under seawater or marine mines. In this thesis we will use (LIBS) to determine the elemental composition of a metal by forming micro plasmas on the surface of a five standard Zn – Al alloy metal targets, both in air and water has been described. In this thesis, two different Nd:YAG laser sources working at 1064 nm are synchronized for underwater measurements by a two-channel pulse generator and steered along the same path by using beam splitter (40/60 % @1064nm) then focused into metal sample immersed underwater surface, while for air measurements a single laser source was used. A pair of optical systems were used , the first one was used to focus the beam on target and the second on as a telescopic system for the detection system which consists of a PI-Echelle spectrometer and ICCD camera.The plasma emission spectrum was recorded at several conditions for both air and water measurements in order to optimize signal to-noise ratio and spectra therefore temporally resolved optical emission spectroscopy is used to investigate the evolution of plasma and spectral line intensity and to estimate plasma parameter such as electron density and plasma temperature as well as the limit of detection using a home built MATLAB programs. The effect of gate time delay and gate width as well as inter-pulse delay has been observed and studied by monitoring the behavior of the spectra lines. For underwater measurements the gate time delay was in the range of (200-1000nsec), inter-pulse delay in the range of (20-100 µsec) and gate width in the range of (1000-5000 nsec) were observed. It has been found that the optimum experimental conditions for the double pulse LIBS under water measurements are 200 nsec gate time delay, 50µsec inter-pulse delay and 1000 nsec gate width. For air measurements the gate time delay was in the range of (200-2000nsec) and gate width in the range of (1000-10000 nsec). It has been found that the optimum experimental conditions for the single pulse LIBS air measurements is 1500 nsec gate time delay and 10000nsec gate width . The plasma temperature was determined using Boltzmann-plot method of Fe I lines observed from samples located underwater and in atmospheric air, a value of 10500+/- 500 k° for underwater measurements were derived as opposed to 11200+/-400 k° in air. The electron density was derived from the line shape data of the stark broadened Hα 656.29 nm and Zn 330.25 nm, a typical values of Ne=8.54014E+17 in air and Ne=4.5418E+18 underwater has been achieved. For quantitative analysis purposes calibration curves for three elements Cu I, Fe I and Mg I has been evaluated. The calibration curves were constructed to estimate the limit of detection (LOD in mass%) , the estimated values of achieved water and air LOD respectively were 0.517795% and 0.035106% for Cu , 0.042374% and 0.013093% for Fe and 0.03933%, 0.001339% for Mg . The presented work has proved the reproducibility of LIBS experiments in detection metals underwater and supports the perspective of its application as in situ analytical technique.