Terahertz radiation enhanced by a laser-irradiating on a double-layer target

An enhancing terahertz radiation scheme, in which a linearly polarized laser pulse irradiates a double-layer target consisting of a near-critical density plasma and an overdense density plasma, is proposed and studied by using the two-dimensional Particle-In-Cell simulations. Compared with that in the single-layer target only containing an overdense density plasma, the results show that the electric field intensity of the terahertz wave passing through the probe point is increased by an order of magnitude in the double-layer target. We find that the electrons coming from the interaction of laser with near-critical density plasma are the origin of enhancing terahertz radiation. These electrons gain high energy through the direct laser acceleration mechanism, leading to the maximum cut-off energy being more than 5 times higher than that in the single-layer target. Besides, the influence of the parameters of the near-critical density plasma on the terahertz radiation is also scanned through a series of numerical simulations, and the robustness of this scheme is verified. This scheme may provide a theoretical and parametric guidance for the generation of strong-field terahertz waves based on the relativistic femtosecond laser irradiation of structural targets.