الفهرس 
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Abstract
A comparative study between single and double pulse-laser induced breakdown spectroscopy (LIBS) was performed on n-type silicon (111) target. A new mobile double pulse Nd: YAG laser at 1064 nm was used throughout the measurements. The experiment was carried out in two ambient gases; air and argon at different pressures of 0.7, 470 and 1000 hPa in air and 470 and 1000 hPa in argon. The ambient gas interacts with the laser beam and the plume, several mechanisms are involved in these interactions, such as, plasma shielding, shock wave production and plasma expansion. Plasma shielding effect reduces laser–material coupling efficiency. However, the induced shock waves increase the coupling efficiency in case of double pulse LIBS. The spectral emission of lines emitted from both the silicon target and that from the ambient gas atoms surrounding the target have been analyzed. In single pulse, at the atmospheric pressures (1000 hPa) the emission intensities of lines emitted from the silicon target have lower values than that obtained in low pressure ( 0.7 hPa) and from the ambient gas ( N I and Ar I lines). It has been found that in case of double pulse LIBS, the emission intensities of atomic and ionic lines are strongly enhanced at higher pressures. A discussion of local thermodynamic equilibrium state is presented. Using Stark broadening of the line profiles of atomic silicon, the electron number densities for single and double pulses are calculated (Ne ≈ 1017 cm-3). Plasma excitation temperature (Te ≈ 5000-7000 K) and ionization temperature (9000-13000 K) are determined from Boltzmann plot and Saha-Boltzmann equation, respectively. The double-pulse laser induced plasma has been studied at different interpulse delay times: 1, 2, 5, 10, 15, 25 and 50 μs. The influence of the interpulse delay time on the signal enhancement of the atomic and ionic lines and the plasma parameters is investigated. Crater depth measurements are estimated via optical microscopy. The results indicated that the crater depth, the atomic and ionic line intensities increase at short interpulse delay time (1-5 µs).