چكيده به لاتين
In recent years, significant advances in the production of short and powerful laser beams have led researchers to pay special attention to the interaction of lasers with plasma. Interaction of plasma with high power laser causes nonlinear effects such as self-focusing, laser filament generation, second harmonic production and terahertz radiation. Also, studying the effect of external applied fields such as magnetic field and electric field to the interaction of laser with plasma has been attracted by researchers. Considering the importance and effect of external field applications as well as the observed nonlinear effects, their role in the interaction of special plasma lasers from the perspective of terahertz radiation production has been investigated in the present study. Terahertz radiation has unique properties and many active and passive applications in areas such as telecommunications, communications, spectroscopy, industry, medicine, security, etc. have been proven and are expanding every day. In this dissertation, the production of terahertz radiation by plasma laser interaction has been studied by two different proposed methods. In the first method, resonant terahertz radiation originated from self-focusing of a super Gaussian laser beam with amplitude modulated in plasma and oscillating electron density index was analyzed. At this stage, self-focusing, generated terahertz field, terahertz power and also efficiency have been calculated. It was found that by adjusting the laser and plasma parameters such as amplitude of density fluctuations, beam order, frequency and modulation period, the efficiency of terahertz radiation increase significantly due to the self-focusing of the laser beam in plasma. In the next step, a magnetic field was applied to the plasma perpendicular to the laser beam propagation. In this case, the magnetic field increased the self-focusing as well as the efficiency of the terahertz radiation significantly. The second method investigates the generation of terahertz radiation induced by the dark hollow beam laser beam when a constant and uniform electric field perpendicular to the direction of laser propagation is applied to the plasma. The amplitude of the field and the small efficiency of radiation produced by dark hollow laser beams in plasma, as well as the ease of producing and applying a constant electric field, are the main motivations of this study. It was found that the application of a constant and uniform electric field, in addition to increasing the size and efficiency of the terahertz field, produces a terahertz field with a special index that has an exclusive and adjustable pattern appropriate to changes in the amplitude of the electric field. Due to the interactions between the transverse profile of the dark hollow laser beams and the electric field, the size of the terahertz radiation field and its efficiency are maximized, which can be used to produce specific and adjustable terahertz frequencies.
