Theoretical Study On The Terahertz Wave Generation Driven By The Two-Color Bi-Elliptical Polarized Laser Field

Because of its unique optical and electrical properties,terahertz waves have broad application prospects in civil and military fields such as physics,biology,public safety inspection,wireless communication,information security,environmental monitoring,nondestructive testing and national defense science and technology.However,it is still a challenging research topic to obtain high intensity terahertz radiation source with controlled polarization state.Terahertz waves driven by circularly polarized and linearly polarized laser fields have been extensively studied,but the properties of terahertz waves generated by elliptically polarized laser field need more research.Based on the photocurrent model,the intensity and polarization characteristics of terahertz waves driven by two-color elliptical polarization laser field are studied theoretically.The main results obtained are as follows:1.The simulation results of terahertz waves generated by co-rotating elliptical polarization laser fields show that when the wavelength of two laser pulses is 800 nm and 400 nm,the dependence of terahertz intensity generated by orthogonal and parallel elliptical polarization laser fields on the relative phase is different.Moreover,the long-axis parallel elliptical laser field can produce linearly polarized terahertz radiation equivalent to the co-rotating circular polarization laser field.Terahertz waves with controlled polarization state and near circular polarization can be obtained by using long wavelength and short period co-rotating elliptical laser field.The analysis shows that the symmetry of laser field is related to the ellipticity in addition to the phase and intensity ratio.By changing the laser ellipticity the residual current value in two orthogonal directions and the relative intensity of the radiated terahertz wave can be controlled.The results also show that the ellipticity of terahertz waves can be significantly improved by the co-rotating elliptical laser field with small ellipticity compared with the two-color linear polarization field.The elliptical laser field provides more degrees of freedom than other driving lasers to control the polarization of the resulting terahertz waves.2.The terahertz waves generated by a two-color counter-rotating laser with high ellipticity(>0.9)and double circularly polarized laser field are compared.The results show that the terahertz radiation intensity is highly sensitive to the ellipticity of the driving laser,that is,the terahertz wave intensity can be significantly enhanced by slightly changing the ellipticity of the double circularly polarized laser field.Moreover,the terahertz polarization state can be controlled by changing the intensity ratio of the elliptical laser field.These phenomena can also be explained qualitatively by the symmetry of the field and the residual current.