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Self-Focusing of Laser Beam in Relativistic Quantum Plasma

Rezaee, Sajad | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45972 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Sadighi Bonabi, Rasoul
  7. Abstract:
  8. 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 studied and it is shown that the ramped density improves the self-focusing of the pulse in comparison to the one with uniform density. Furthermore, the dependence of the beam width on the degree of the ramp is studied. It is recognized that the increase in the degree of the ramp results in reduction the self-focusing length and also causes faster decreasing of the beam width and the minimum spot size. Additionally, it is found that higher initial density of plasma improves the self-focusing. The comparison between the results in quantum and classical plasmas shows that the self-focusing length for the thermal and cold cases compared to the one in classical plasma is improved by 66% and 46%, respectively. Thereafter, self-focusing is studied in collisional quantum plasma and the results shows that by assuming the collisions between the ions and electron, the beam width oscillates with higher amplitude relative to the collisionless one and the pulse is diverged at a certain depth in the plasma. It is also found that by increasing the collision frequency and plasma density, faster energy absorption in plasma occurs. Consequently, the pulse width oscillates with larger amplitude and it is defocused faster. It is realized that in the collisional case, such as the collisionless one, by increasing the plasma density the minimum spot size is reduced
  9. Keywords:
  10. Relativistic Self-Focusing ; Quantum Plasma ; Ramped Density Profile

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