چكيده به لاتين
The Terahertz (THz) frequency regime invisible to naked eye lies between microwave (photonics) and infrared (electronics) frequency regions in the electromagnetic spectrum. The THz technology has woken up the immense potential interest for its alications in many areas like security, medicine, broadband THz communications, spectroscopy, etc. There are many methods to generate THz radiation. Non-plasma based techniques to generate THz (such as electro optic crystals, semiconductor and photoconductive antennas, etc.) have some drawbacks such as low conversion efficiency, narrow bandwidth of emitted THz radiation, and material breakdown material in high power laser pulses. In contrast, plasma is a promising medium to generate strong THz radiation which can overcome the damage problem of neutral materials when the energy of lasers is high. In the thesis, we work on plasma based THz radiation generation schemes where plasma as a nonlinear medium can handle very high power lasers which this leads to generate THz radiation with high efficiency and also plasma has an added advantage of not having damage limit. There are various schemes based on laser plasma interaction, THz radiation generation by beating of two lasers of different frequencies and wave numbers in plasmas has shown tremendous potential in terms of amplitude of THz radiation, efficiency and tunability. In the present thesis, laser with different profiles such as Gaussian, super-Gaussian, spatial triangular and cosh-Gaussian spatial are utilized to generate efficient THz radiation. Plasma density riles are proposed to introduce extra momentum (in propagation direction) to achieve exact phase matching condition for maximum energy transfer between nonlinear ponderomotive force (at difference frequency) and nonlinear current which is responsible for the excitation of THz radiation. An oblique static magnetic field is introduced to improve the tunability and to increase the efficiency of THz radiation.
