Document Details

Document Type : Thesis 
Document Title :
Theoretical study of the collisional ionization mechanisms based on laser resonance saturation in alkali vapours
دراسة نظرية لآليات التأين التصادمي المبني على التشبع الرنيني بأشعة الليزر في أبخرة القلويات
 
Subject : Physical Chemistry 
Document Language : Arabic 
Abstract : A previously developed numerical model depends on Laser Ionization Based On Resonance Saturation (LIBORS) is; firstly applied to interpret the experimental measurement which are carried out to study the plasma formation in laser excited rubidium vapor at the first resonance transition 5s-5p and the 5p-nl transitions. The model solves numerically the time dependent Boltzmann equation and a set of rate equations that describe the change of the ground and excited states population of the atomic rubidium vapor under the experimental condition adopted in the measurements. The model solves also the rate equations that represent the change of the formed ion current densities. The calculations are carried out to determine the time evolution and laser power dependence on the electron energy distribution function as well as the electron density which is created during the interaction. The results of this study revealed the exact contribution of each process in the formation of the plasma species. Secondly; the model is modified to include processes responsible for the generation of more initial free electrons as well as ion current viz, photo-ionization, Hornbeck Molnar ionization and ion-pair formation. The modified model is then applied to calculate the individual effect of each of these processes on the EEDF, the electron density as well as this ion current at different values of irradiation time and laser power. In doing so, comparison is performed between the calculated values of these parameters in the presence and absence of each of these processes. This comparison indicated the role that each process plays in the growth of the free electron density and the molecular and atomic ion currents and in turn in the formation of plasma in the atomic rubidium vapor. In addition, the results of these studies clarified that initial electrons are effectively created from the associated and Penning ionization processes and are heated by super elastic collisions. This means that under the experimental conditions that uses laser radiation of low power (50-500mW) and a relatively low atomic density (1013 cm-3), the dominant processes for plasma formation are collisional ionization and collisional excitation processes. Moreover, the study of the EEDF presents the pronounced contribution of the photo-ionization of the excited vapor atoms in producing free electrons with energies >1.0 eV. The results of negative ion current results from ion-pair formation process showed also a significant evidence for its occurrence rate which increases as the laser power increases. 
Supervisor : . Yosr E. Gamal 
Thesis Type : Doctorate Thesis 
Publishing Year : 1430 AH
2009 AD 
Number Of Pages : 182 
Added Date : Monday, September 9, 2013 

Researchers

Researcher Name (Arabic)Researcher Name (English)Researcher TypeDr GradeEmail
خلود احمد حمامHamam, Kholoud AhmedInvestigatorDoctorate 

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