الفهرس 
Role of physical processes in the production of sodium plasma by laser Ionization based on resonance saturation
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Abstract
This work is based on the modification of a previously developed model by (Mahmoud and Gamal, 1995). This model was initially developed to study theoretically the time evolution of the energy distribution of free electrons created by collisional ionization of sodium vapor resonantly excited with CW laser due to different physical mechanisms basing on laser Ionization based on resonance saturation (LIBORS) technique. The modification is devoted to include into the model an ionization process which acts to increase the seed electrons density namely tri-atomic associative ionization process. The cross section of this process was determined experimentally by tapalian and smith (tapalian and smith, 1993) in their measurements of the trimer ion yield in sodium vapor. In this experiment two continuous dye lasers are tuned to the transitions Na (3s)-Na (3p) (589 nm) and Na(3p)-Na (4d) (569 nm) at intensities of up to 100 W/cm2. Under these conditions associative ionization (AI) processes involving high energy states (Na(4d), Na(5s)) are studied, for example AI collision of Na(4d) atoms with Na2 ground state molecule (present at {u2248} 0.5% percent in the atomic beam) resulting in Na3+ trimer ions. Accordingly an additional term refers to this process is included into the numerical model. This in turn implied the modification of the rate equations which describes the variation of the excited states population, ion currents as well as the electron energy distribution function (EEDF). Following to this modification the model is applied first to calculate the tri-atomic ions current against the density of the sodium vapor for different exposure time intervals taken into account the experimentally determined cross section given by tapalian and smith