Theoretical Study On The Polarization Characteristics Of Terahertz Radiation From Gases Driven By Strong Laser Fields

Terahertz wave is a special and significant electromagnetic radiation between millimeter wave and far infrared light.Terahertz waves have very attractive application prospects in biomedicine,imaging,communication,remote sensing,etc,and have attracted widespread attention and research interest.Among the many methods of terahertz generation,femtosecond laser-induced gas plasma is an important broadband terahertz radiation source.This thesis mainly focuses on the investigation of the polarization characteristics of terahertz wave generation by two simple kinds of two-dimensional driving lasers.The main contents and results are as follows:Firstly,based on the photocurrent model,we theoretically simulate the polarization law of terahertz waves radiated by the interaction between a monochromatic elliptical polarized laser and atomic argon.The results show that the polarization state of the terahertz wave can be fully controlled by the parameters such as the ellipticity of the driving laser,the carrier envelope phase,and the polarization angle.It is very important that circularly polarized terahertz radiation can be obtained with this type of laser pulse.Secondly,the polarization characteristics of terahertz waves radiated by a two-color laser field(? + 2?)composed of two linearly polarized lights are investigated.The simulation results show that the phase of the two laser pulses has a great effect on the polarization state of the radiated terahertz wave.The terahertz radiation is linearly polarized for the phases of 0? and 0.5?,and does not depend on thepolarization angle between the two linearly polarized lasers,which is consistent with existing results.More importantly,we find that for other phases,the two-color laser field can produce elliptically polarized terahertz waves.The ellipticity of the terahertz wave increases with the increasing of the polarization angle between two incident beams of driving laser field,and reaches a maximum value at about 85 °,this is very similar to the polarization law of the terahertz wave radiated by the laser pulse focuses on the air in the experiment.In this thesis,since the single atom calculation does not consider the change of the polarization state of the 2? pulse caused by the molecular-induced birefringence,it is worth more research work to verify the results of this thesis.