Sharif Digital Repository

Optimum conditions for the proton acceleration using radiation pressure acceleration in light sail regime is investigated using particle-in-cell simulations. Simulations results show that for a laser pulse with a dimensionless laser amplitude of a0 = 31 using circularly polarized laser pulse with sin2 shape at perpendicularly incidence are the best. Effect of two pulses with different duration and different amplitudes (a0 = 25; a′ 0 = 13) is also investigated in the condition of equal total energy of them to the single pulse and amplitudes of both of them are less than the single efficient laser pulse amplitude. Best delay time between two pulses was found by changing the delay time in... 

Due to the interaction of high power lasers with over-dense plasma high harmonics are generated. The increase in harmonics cause an increase in frequency to the level of x-ray frequency and is thus a new method for creating x-ray lasers. In this research, we seek to understand the physics of this problem . Some theories try to explain this phenomenon based on the Doppler shift caused from the reflection of the laser beam from surface of the plasma, which oscillates with relativistic velocity.some try to explain this phenomenon based on the similarity with synchrotronic emissions. In this research, the main theories on this subject are reviewed, and a modelling of the emission caused by the... 

Deep reactive ion etching is one of the most used techniques for manufacturing micro-structures. The most popular silicon DRIE technique is Bosch process. Ability to manufacture high aspect ratio features made Bosch process the main technique for developing micro-electromechanical devices. Dry etching is a combination of physical and chemical processes. The chemical processes play a very important role due to their speed of material removing and also due to their high selectivity. Also chemical processes are responsible for development of passive resist layer on the surface. On the other hand, if not controlled properly it can reduce anisotropy, resulting in a low quality etch. In this... 

One of the most important applications of plasma is etching of substrates. This process is the key element of microfabrication. In order to improve the microstructures quality, it is necessary to improve plasma etching process. Therefore different methods have been developed to make etching process more efficient. The latest method is Bosch-process etching method. In this project to understand the effect of input parameters, Bosch-process etching of a PMMA substrate is simulated. Based on the governing equations, the problem is divided to four parts. First, by developing a heuristic approach to solve Maxwell’s equations numerically, electric and magnetic fields in the chamber are determined.... 

In this thesis, plasam kinetic aspects causing production of high-energy super-thermal particles in strongly nonlinear perturbations, including relativistic electron waves and shock waves occurred respectively in astrophysical and laser produced plasmas, have been studeied. Importance of kinetic simulations in this area has been demonstrated. In this respect, passing serious challenges, we have prepared a kinetic particle-in-cell (PIC) code and applied it within our supplied computational-resources. Relativistic electron waves produced via interaction of laser with tenouse plasmas have been deeply studied. These studies have resulted in new findings in fluid description of these waves,...