Sharif Digital Repository

In this work we studied the interaction of a high frequency electromagnetic wave in under relativistic and relativistic regims with a plasma taking into account of the ponderomotive fo per unit volume acting on plasma electrons.In under relativistic regim at first we assumed the plasma is collisionless, unmagnetized and non isothermal which occupying the semi - space Z 0 .We found the nonlinear differential equation for the electric field using theMaxwell and hydrodynamic equations.We obtain the profiles of the electric and magnetic fields in plasma and we see that the electron density oscillations appear highly peaked. Then in this regim a direct one dimensional (1D) procedure for... 

Using field assisted dissociation model and with a classic view the dissociation probability is calculated when it a molecule is exposed with a Ti:sapphire laser with wavenumber of 800nm and the energy of . using gradient optimization method we find a tailored two rectangular laser pulse for controlling the dissociation of C-H bond of . Using classical method reduced the complicacy of solving schrodinger equation. In our optimization method in contrast with the usual controlling method experimental data is not needed and this reduced the controlling costs.

 

Conversion of Methane molecule to valuable heavier hydrocarbon and hydrogen by using of short pulse lasers is investigated. The dynamical information of molecule such as orientation, dipole moment variations with binding length, and potential energy levels are initially produced by using Gaussian software. Based on this information the Schrödinger wave equation for this polyatomic molecule is numerically solved. Then by selecting the various laser parameters and installing of them in the Hamiltonian of the mentioned system, the dependence of hydrogen transition and separation probability on these parameters are investigated. In this work by radiating of the laser beam along the C2 symmetry... 

Artemia (brine shrimp) is a genus of crustaceans that lives in saltwater and due to having unique features, in producing the food and nutrients needed for larvae and other types of farmed sea creatures, is of great importance. In its natural environment under certain conditions, Artemia produces cysts that float at the water surface and are driven ashore by wind and waves. These cysts are inactive and do not develop further as long as they are kept dry. Upon immersion in seawater, the biconcave cysts hydrate and become spherical and, within the shell, the embryo resumes its interrupted metabolism. After about 20 h the outer membrane of the cyst breaking and the embryo appears, surrounded by... 

Nd:YAG laser is one of the most applicable lasers on laser researches where it’s basic wavelength and higher harmonics are used on different laser projects. It should be realized that it’s basic output has a wide pulse duration and lower peak power. Therefore, in order to increase the peak power the pulse duration is reduced by Q-switching.
In this project, in the first step, based on flash-lamp pump Nd:YAG laser a 600 mj energy per 60 µs pulse is constructed. Then a pulse duration is shorten by order of more than 3000 via electro-optics Q-switching system where we could reach up to 19 ns pulses and laser peak power is increased up to several megawatts  

Resent advances in ultra-intense short-pulse lasers and their numerous applications stimulated the research activities in important fields such as generation of high-energy electron and ion beams, monoenergetic electron beam, monoenergetic ion beam, X-ray emission, terahertz radiation, high harmonic and attosecond pulses generation. In all above mentioned applications the relativistic electrons behavior especially the electron density distribution and the velocity of electrons play an important role.
Investigating the behavior of relativistic electrons which are generated in the interaction of high power femtosecond lasers with plasma and their related applications is the main purpose... 

The purpose of this project is to investigate the production of nano-micro metallic particles—of different elements—with different characteristics in size and optical property by employing a pulsed laser ablation processes in liquid medium. In this study, the means by which we build the laser, the experimental arrangement of the pulsed laser ablation process, the measurement of the absorption spectrum of generated nano-micro particles as well as the size of the particles are discussed.
To satiate this aim, we have expressed the manner of constructing the Nd:YAG laser, the power supply circuits, along with its optics. This laser has some advantages such as high energy ~700mj, good... 

Nowadays almost all the research laboratories use femtosecond lasers, and Ti: sapphire laser is the most popular among them. Therefore, in this thesis, a Ti: sapphire pulsed laser with z-fold cavity with output of 50 fs and repetition rate of 100MHz has designed and simulated. Therefore, in the first chapter, introduction to the theory of ultrashort pulses and situation to create these pulses are presented. In addition, as regards to produce of short pulses, it is necessary to set laser in cw mode, in the second chapter we have investigated laser in cw mode. So, in this chapter, rate equations of gain medium, the stability zone of the laser, manner of removing astigmatism in the cavity,... 

In this work a theoretical overview of Parity-Time symmetry and its application in multilevel atomic systems are presented. Because of equivalence between the Schrodinger equation and the paraxial propagation equation, complex index of refraction plays the role of complex potential. On the other side, the possibility to manipulate loss, gain and the index of refraction simultaneously, Optics is a fertile ground to investigate Parity-Time symmetry and one of this symmetry’s applications is reduction of loss in optical systems. Furthermore, In order to realize Parity time symmetry a four level atomic system under electromagnetically induced transparency condition is proposed. Optical gain... 

In this thesis, conversion of methane into heavier hydrocarbons was performed by nanoparticles-assisted nanosecond laser induced plasma. Nickel oxide nanoparticles was synthesized by sol-gel procedure and packed into a compact tablet after drying and used as a target in a two BK7 windows-camber with pressure of 1500 mbar. Methane was introduced to the chamber and two different nanosecond lasers namely, Nd:YAG (λ=1064 and 532 nm) and KrF (λ=248 nm) were radiated. Interaction of the gas with the plasma produced by metal nanoparticles and the thermionic emissions due to the inverse bremsstrahlung caused conversion of methane to the heavier hydrocarbons. These conversions can also promote by... 

The aim of this thesis is calculating soliton pulse propagation in fiber optic and its interaction with plasma to generating high accelerated electrons for radiotherapy. By chirped pulse amplification technique in the new generation of table-top lasers, the intensity of laser beam could be increased up to . A high gradient electric field more than is generated by the interaction of this high intense laser beam with plasma gas. In these high gradient fields electrons can be accelerated. These accelerated electron beam can be played an important role in radiotherapy. In this project by using general pulse propagation equation in linear and non-linear medium and solving non-linear... 

In this research, using a hydrochemical model alongside three dominant instabilities of shape, Bjerknes and diffusion, the effect of ambient parameters on the single bubble sonoluminescence (SBSL) in Sulfuric Acid (SA) is studied. The phase diagrams of the bubble in the (R0 − Pa) space are presented, and the parametric dependence of the light intensity is discussed. In a part of this research a hot plasma core is considered at the center of the bubble. The study of ambient temperature shows that in contrast to water, the calculated thermalbremsstrahlung mechanism of light emission at the fixed degassing condition of high SA concentrations shows that with increasing the temperature of aqueous... 

In this thesis the conversion of methane into higher hydrocarbures using pulsed nanosecond lasers has been studied. The lasers of 532 nm of second harmonic of Nd: YAG, 355 nm of 3rd harmonic of Nd: YAG and 248 nm of KrF have been used in this project. Acetylene, ethylen and ethane have been detected using gas chromatography detection system, which showed acetylene as a dominant product. For each wavelength the amount of the laser energy and the fraction of secondary products have been measured. Also the dependence of amount of produced components on chamber pressure has been studied for 355 nm laser. During the irradiation time of methane no considerable changes in temperature and pressure...