Document Details

Document Type : Thesis 
Document Title :
Study of the effect of laser characteristics on the threshold intensity of molecular Nitrogen gas breakdown induced by CO2 laser radiation
دراسة تأثير خصائص أشعة الليزر على الشدة اللازمة لانهيار غاز النيتروجين الجزيئي المستحث بواسطة أشعة ليزر ثاني أكسيد الكربون
 
Subject : LASER 
Document Language : Arabic 
Abstract : During the last decades of the previous century laser equipment are extensively developed . This in turn attracted a great importance of these equipments where they are considered to be not merely an important invention locking for an application but an important technical system that found many applications . It is possible to obtain laser sources that operate with wavelengths covering a range from the far infrared to the ultra-violet at very high intensities . Accordingly this attracted the researchers to study the phenomenon of breakdown induced by laser radiation that received various applications in different fields . One of these fields is the environmental application that depends mainly on the spectral emission results of the formed plasma in the breakdown region induced by laser radiation in air to determine the pollution constituents. Since air is mainly nitrogen (80%) , therefore the experimental studies are directed to measure the threshold laser intensities of nitrogen using wavelengths in the far infrared , visible and ultraviolet regions . These studies clarified a distinctive contradiction between the measurements of the threshold intensities that carried out in the infrared region . Therefore this research aims to investigate the results of the measurements of the threshold intensities variation with the gas pressure to determine the physical processes that contribute to the breakdown phenomenon at different pressure values and its correlation with the threshold intensity. In doing so a numerical model is applied which is previously developed by Evans and Gamal (1980) and modified by Gamal et al (1987).This model solves numerically the time dependent Boltzmann equation for the electron energy distribution function simultaneously with a set of rate equations that describe the variation of the excited states population. The model takes into account the physical processes that expected to take place in the focal volume during the impact of the laser radiation with the nitrogen molecules. The pulse shape and beam size are determined according to the considered experimental measurements that carried out to investigate the variation of the threshold intensity as a function of gas pressure given by Camacho et al (2007). In this experiment a CO2 laser radiation operating at wavelength of 9.621µm and pulse duration of 60.0 ns is used to irradiate molecular nitrogen over a pressure range of 26.0-760.0 torr for two experimental conditions namely; the presence and absence of initial electron density . Considering these physical processes with their rates and coefficients of the physical processes as electron energy , a computer program is run to obtain a relation between the threshold intensity and gas pressure for the two mentioned experimental conditions. The calculated threshold intensities showed a reasonable agreement with those experimentally measured ones in both cases . Moreover, the calculated electron energy distribution function at different values of gas pressure showed the important role played by the vibrational excitation where the process is found to act as a capture for electrons having energy of 2.0-3.0 eV. 
Supervisor : Yosr E. Gamal 
Thesis Type : Master Thesis 
Publishing Year : 1430 AH
2009 AD 
Number Of Pages : 167 
Added Date : Thursday, September 19, 2013 

Researchers

Researcher Name (Arabic)Researcher Name (English)Researcher TypeDr GradeEmail
عزة محمد الغامديAl-ghamdi, Azzah mohammedInvestigatorMaster 

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