Document Details

Document Type : Thesis 
Document Title :
A numerical study of the mechanisms of breakdown and damage in solid materials induced by femtosecond laser pulses
دراسة عددية لآليات الانهيار والضرر في المواد الصلبة المستحث بنبضات من ليزر الفيمتوثانية
 
Subject : X-Ray Laser 
Document Language : Arabic 
Abstract : Computations are carried out to determine the threshold intensity for breakdown and damage in fused silica by ultra short pulses of laser radiation according to the experimental measurement considered in this analysis. The study adopted two different approaches; firstly numerical model that solves the rate equation for the variation of the electrons density during the pulse duration. The model considered multiphoton ionization and electron collisional ionization as electron gain processes. Besides, electron loss processes such as electron diffusion out of the focal volume and electron recombination are also considered in this model. Secondly, applying Fokker-Plank equation that gives the electron energy distribution function from which the electron density in determined under the same experimental condition. Comparison between the calculated thresholds and the measured ones showed a reasonable agreement over the experimentally tested pulse range (400fs-2.8ps).At the ultra short laser pulses, however ,less than 400 fs a the analysis takes into account the temporal and spatial variation of the laser intensity in the focal volume. In this case the propagation length of the pulse in the focal volume is considered in the variation of the laser intensity. In addition the results give an understanding on the physical processes responsible for the breakdown and damage in fused silica as a function of the laser pulse length as well as the optical system used in the measurements. The analysis also clarified the spatial variation of the electrons density and laser intensity along the radial and axial distances of the focal volume that gives a real picture for the plasma location and size according to the pulse length range tested experimentally. On the other hand, Fokker-Plank model gives a detailed description of the electron energy distribution function as a function of the laser pulse for each value of the numerical aperture, as well as the high electrons density regions that found to be located at the low electron energies corresponding to the energy gap range. Moreover, the study gives the temporal evolution of the electron density which showed the important role played by the photo ionization process in the breakdown phenomenon. For completeness the time variation of the electron mean energy showed the correlation between the ionization rate and process responsible for electron growth as a function of the laser pulse length. 
Supervisor : Yosr .E.Gamal 
Thesis Type : Master Thesis 
Publishing Year : 1430 AH
2009 AD 
Number Of Pages : 155 
Added Date : Thursday, August 29, 2013 

Researchers

Researcher Name (Arabic)Researcher Name (English)Researcher TypeDr GradeEmail
هند محمد الغامديALGAMDI, HIND mohammedInvestigatorDoctorate 

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