Sharif Digital Repository

In this project , the dissociation of methane in the presence of Ti:Sapphire laser with parameters of 1014wcm-2, 800nm wave lengths and 100fs pulse width have been investigated theoretically, by using the Gaussian03 package –computational chemistry program that is capable of predicting many properties of atomic and molecular systems. It is based upon the fundamental laws of quantum mechanism. By considering some limitations in approximate techniques and incapability of advancing them, numerical calculation of solving the time dependent Schrödinger equation in order to improve the results and find more quantum dynamic information is applied. Therefore at first, by Gaussian03 package some of... 

Plasma-based accelerators are capable of producing compact and high energy electron sources in much shorter distances than conventional accelerators. Electron will be trapped and accelerated to higher energy by two pulses as compared to the single pulse case. The aim of the present work is to take up a detailed analytical study of a novel idea of wakefield amplification making use of two laser pulses copropagating one behind the other, with a fixed distance between them. However, we attempt for enhancing the wake field and hence the electron acceleration by employing different shapes of the laser pulses  

In general cases, the generated electron beam with interaction of high intense and ultra short laser with gas plasma targets has large distributed energy spectrum (100%) that is called Quasi-maxwellian energy spectrum. Recently, in some experimental and 3D-PIC simulation results, a narrow band electron energy spectrum has observed that is called Quasi-monoenergetic electron. We approximated that these electrons have Gaussian distribution. High quality quasi-monoenergetic electron beam can focus in small spot. Therefore, there are many applications such as medical applications, crystallography with electron scattering, spectroscopy with soft energy and ultra fast x-ray, photonuclear... 

Copper vapor Laser is one of the strongest and the most efficient visible laser with high repetition rate. It has been the subject of interest in research, industrial and clinical applications. It’s oscillating lines with 510.5 and 578.2 nm between resonance level and metastable level is acting as pulsed type laser. The problem with this laser is its high operating temperature of 1500 C. This high operating temperature could be reduced by using copper halides, where the temperature decreases from 400 to 500 C. The produced heat will first produce the molecular vapors, then the release and excitation of copper occurs with electrical discharge.
In the present study the effect of... 

Quantum interference and coherence could change the optical response of media and results several effect such as electromagnetically induced transparency (EIT), Lasing Without inversion (LWI) and optical nonlinearityenhancement.In Quantum Computing, by using Quantum coherence, one can producedecoherence free sub-space whichhasoutstandingapplications in this field.
In this work optical bistability behavior studied in two coupled quantum dots which resembles a three-level V type atomic system under influence of squeezed state reservoir. Spontaneously generated coherence (SGC) is responsible for Quantum interference. The squeezed state radiation could break the coherence in media and make... 

Sonoluminescence is called a phenomenon in which a gas bubble is trapped in an antinode of a pressure field by a driven periodic acoustical field in a fluid and oscillations and at the end of each collapse, emits a flash. For this emission various conditions for stability must be satisfied, like diffusion stability, shape stability and positional stability. Another method to produce the bubbles is applications of a focused laser beam. In this method, a laser pulse is focused into a transparent buffer liquid like water and bubbles which are induced by the laser are so called Laser Induced Single Cavitation Bubble Luminescence (LI-SCBL). In the presence of the laser, the fluid acts as... 

With the invention of the Chirped Pulse Amplification (CPA) technique in 1985, it became possible to amplify ultra-short laser pulses to high intensities with suitable pre-pulses contrast. By considering the importance of the short wavelengths radiation sources, the interaction of the intense laser with dense plasma is one of the most promising routs to reach this goal.
This thesis is devoted to theoretical studies of the interaction of intense laser pulses with solid-state targets. The Relativistically Oscillating Mirror (ROM) and the nanobunching regime models, which introduced in 2006 and 2010 respectively, are presented and discussed. The reflection of a laser pulse from an overdense... 

The phenomenon of relativistic self-focusing in nuclear fusion and laser-plasma interactions is very important. Under the influence of this phenomenon, the laser beam can move in plasma a few Rayleigh lengths and the interaction efficiency is improved. The relativistic self-focusing in inhomogeneous, homogeneous, collisional and collisionless plasmas has been studied in various conditions of plasma and laser in classical physics. In this thesis the propagation of a laser pulse at the X-ray wavelength range and its relativistic self-focusing in quantum plasma is investigated by numerical simulations. Initially, the interaction with a collisionless ramped density profile plasma target is... 

In this dissertation, a system consisting of two oscillating and amplifier lasers was designed and constructed. The aim was to use this combination to measure important parameters of CuBr vapor laser. Therefore, two separate Thyratrons switching by a two-pulse control circuit with an arbitrary time delay have been used. Due to the sensitivity of these lasers to tube pressure, two quartz tubes with specific designs was used. This enables us to get a proper vacuum as well as to prevent from impurities in the windows, in a short range of time. In this system, the output light from oscillator is led to the amplifier and after a proper delay time, amplifying was observed.
Based on... 

Ionization probability of Cl2 molecule is studied by irradiation of 800 nm Ti: Sapphire laser pulses at intensities of 1014 Wcm-2 to 1016 Wcm-2 with the Gaussian package. Molecular orbital symmetry and orientation of the molecule dipole moment with laser field polarization axis are very effective in ionization probability. The results show that the most ionization probability for the intensity of 1014 wcm-2 is at 900 and also 50 at intensity of 1016 wcm-2. Due to the lack of intrinsic dipole moment, variation of dipole moment with the intensity, bond length and time evolution of dipole moment are investigated. It is found that there is a linear dependance of these parameters with ionization... 

This thesis deals with the theoretical and experimental investigation of quantum interference and coherence, and electromagnetic induced transparency (EIT) in multi-level atomic systems such as hot and cold Rb atoms, semiconductor quantum dots and wells. Optical properties of atomic media in presence of coherent laser fields and incoherent fields are studied.
Theoretical studies verify the crucial role of atomic coherence due to quantum interference in modifying optical properties of atomic media. Suitable and efficient models based on multi-level atomic systems to investigate the optical properties and, optical bistability and multistability are proposed. The most advantages of these... 

Considering the generation of quasi-monoenergetic electrons with femto-second Lasers, producing X-Rays using these electrons is of interest. Lately, higher efficiencies of x-ray generation have been demonstrated by bombardment of different metal slabs, with quasi-monoenergetic electrons instead of Maxwellian electrons. The goal of this research is to study how changing the geometry of the target will affect efficiency and angular distribution of generated X-rays. The electron source is defined using a theoretical model and experimental data. MCNP4C code has been utilized to simulate the collisions of these electrons with a metal target. Intensity and quality of generated X-Rays are obtained... 

By using Mie theory and experimental data for complex refractive index of Au and Ag nanoparticles, the scattering and absorption efficiency of these nanoparticles in silicon medium (crystalline, Polycrystalline and amorphous silicon) was investigated. It was shown that Ag and Au nanoparticles can be used for confine the light, in desired wavelength band, inside the solar cell.The optimum nanoparticle size for using in this kind of solar cells was about 70-80 nm. In amorphous silicon confined photons cannot participate in electron-hole generation so the application of these metal nanoparticles in this kind of solar cells cannot be useful. Also the complex refractive index for equivalent... 

A coupler free scheme for directly exited surface polariton (SP) using a negative-index metamaterial (NIMM) with a bottom layer of N type quantum emitters is presented. It is shown that by suppressing the ohmic loss the giant field enhancement could be achived in a broad electromagnetically induced transparency (EIT). And this field enhancement cause the excitation of surface polariton at the NIMM-Quantum emitter interfaces. For large range of probe detuning in EIT position and the tunable excitation of SP could be accomplished for special probe angle.It is revealed that the linear and nonlinear optical properties could be controlled effectively by modulating the phase of the microwave... 

Nd:YAG laser is one of the most applicable laser for researches and development where it's basic wavelength and harmonics are used on different laser project. It's basic output has a wide pulse duration and low peak power ,therefore in order to increase the peak power the pulse duration is reduced by Q-switching.In this project by means of passive Q-switch technique an energy equivalent to 500 mj with 10to 20 ns pulse duration is extracted from the oscillator and the output energy is amplified to about 850mj in a single pass through amplifier. In this project we used saturable absorber for Q-switching because it is more optimum and simpler than other Q-switching techniques like... 

With the invention of the Chirped Pulse Amplification (CPA) technique in 1985, it became possible to amplify ultra-short laser pulses to high intensities with suitable pre-pulses contrast. By considering the importance of the short wavelengths radiation sources, the interaction of the intense laser with dense plasma is one of the most promising routs to reach this goal.This thesis is devoted to theoretical studies of the interaction of intense laser pulses with solid-state targets. The Relativistically Oscillating Mirror (ROM) models, which introduced in 2006, is presented and discussed. The reflection of a laser pulse from an overdense plasma surface as the oscillating mirror, to the speed... 

The aim of this thesis is to investigate one of the novel methods of accelerating particles such as electrons acceleration method. In intense femtosecond laser plasma interaction, a Wakefield is formed that trap electrons and accelerating them which this process will be fully addressed in this project. Due to the recent rapid development of technology for producing over dense plasma in laser-plasma interaction process in smaller sizes and the possibility of nuclear fusion reactions, the quantum effects are important and must be taken into account quantum effects in plasma. We study quantum effects by introducing the Bohmpotential and assuming the plasma as a one dimensional electron fermi... 

Distributed feedback dye lasers are among the suitable candidates for spectroscopic applications due to their capability of producing widely tunable picosecond pulses in UV-IR region. However, the pulsewidth sensitivity of the laser to pump intensity fluctuations hinders its suitability for precision applications. In this thesis, by utilizing widely used Self Q-Switching model, we showed that if the dye solution is pumped by a narrow (sub-nanosecond) pulse, the laser can operates in the single-pulse output mode with a better stability over a wide range of pump intensity. After that, we used a dynamical model based on the induced polarization and Maxwell equations, where the obtained results... 

In this study, how to create spectral singularity in amplitude and phase in the proposed hybrid system and controllable propagation of plasmon waves of nonlinear polaritons has been investigated. For this purpose, a nonlinear hybrid system consisting of an atomic layer and a metamaterial layer is investigated. The atomic layer can be a gaseous system like rubidium atoms that are cooled to few Kelvin by magnetic systems,or these atoms can be thought of as charged particles that are impurity doped into a clear crystal and cooled to a temperature of a few Kelvin.This quantum system is placed on a metamaterial layer in the form of Al2O3 which has a nano-fishnet structure.This frequency... 

Over the past two decades, scientists have been intensely interested in the development of metallic nanostructures for their applications in industry and medicine due to their attractive optical properties resulting from surface-localized plasmon resonance (LSPR).In this Thesis, plasmonic resonance modes in bridge dimer (Gold and Silver) are numerically investigated. Without the junction, A high-energy resonant mode called the bonding dimer plasmon (BDP) mode appears in the optical spectrum of the dimer, which is caused by the coupling of each of the nanoparticle plasmon modes. But in bridge dimer, two resonances called screened bonding dimer plasmon mode (SBDP) and charge transfer plasmon...