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The influence of magnetic fields of lasers on the generation of terahertz radiation by an interaction between two-color lasers and plasmas is investigated from theoretical analysis and particle-in-cell simulation. Analytical expressions of the terahertz radiation field for both the laser propagation direction and the laser polarization direction in the presence of the magnetic fields of the lasers are obtained. It is found that the magnetic fields of the lasers only have a contribution or enhancement on the terahertz radiation field in the laser propagation direction, while it has no influence on the terahertz radiation field in the laser polarization direction. The feasibility of the theoretical result is validated through particle-in-cell simulation. This investigation shows that for terahertz radiation in the laser propagation direction, the effect of the magnetic fields of the lasers must be considered. Moreover, an external magnetic field is needed to modulate the terahertz radiation in the laser polarization direction since the magnetic fields of the lasers have no influence on it. [ABSTRACT FROM AUTHOR]

The generation of vortex terahertz (THz) radiation by the interaction of a two-color Laguerre–Gaussian (LG) laser with plasmas under an external magnetic field is investigated theoretically and numerically. It is found that the vortex THz radiation with good monoenergetic properties can be generated successfully, and the orbital angular momentum of the LG lasers can be transferred to the radiation. In this scheme, the external magnetic field can not only enhance the intensity but can also break the spatial distribution symmetry of the vortex THz radiation. With the increase in the initial plasma density, the intensity of the vortex THz radiation increases significantly before reaching saturation and the spatial period of the radiation decreases, which indicates the monoenergetic peak of the vortex THz radiation can be well controlled through the initial plasma density. The relevant conclusions are verified by two-dimensional particle-in-cell simulations. [ABSTRACT FROM AUTHOR]