Thesis (M.Sc.) - Cairo University - Faculty of Science - Department of Physics

The spectral emission from plasmas of pure Mo, Mo-Ni-Cr alloys and Li-Cu alloys following irradiation by different Nd: YAG laser beams were investigated. The study was done with the laser beam at its first harmonic (1064 nm), 206 mJ, 7 ns duration pulse, repetition rate 10 Hz (Type Q- switched Nd:YAG laser at National Institute of Laser Enhanced Science, Cairo University) and the second harmonic (532 nm ), 300 mJ, 2 ns duration pulse and repetition rate 10 Hz (Type Quantal Brilliant Q-switched Nd:YAG laser at Philipps Universitat Marburg, Germany) in open air at atmospheric pressure. The radiation emitted from the target in the local thermodynamic equilibrium (LTE) was analyzed and the temperature of the plasma was calculated by the Boltzmann plot method. The electron number density (Ne) was determined from the Stark broadening of the emitted spectral line. The comparison of the electron densities at different neutral molybdenum lines (465.5, 498, 517and 550 nm) with those from hydrogen HÜ-line (656.3 nm) showed good agreement. The study included also the variation of the electron densities and electron temperatures with the delay time, the laser fluence and the distances from the target surface. The aim of the work is to check the self-absorption and to correct for the intensity of the spectral lines and hence to improve the accuracy of the electron temperature and the electron density results. It was found that the neutral molybdenum lines suffer from self-absorption and hence a correction for self-absorption was done. The corrected temperatures against self-absorption were measured at different delay times ranging from 2 to 5 os. The electron density and the electron temperature were also measured for Mo-Ni-Cr alloys and Li-Cu alloys at different laser fluencies and were compared with the results from pure Mo targets

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