THz transition radiation of electron bunch laser-accelerated in long-scale near-critical density plasmas

Direct laser electron acceleration in near-critical density plasma produces collimated electron beams with high charge $Q$ (up to $μ$C). This regime could be of interest for high energy THz radiation generation, as many of the mechanisms have a scaling $\propto Q^2$. In this work we focused specifically on challenges that arise during numerical investigation of transition radiation in such interaction. Detailed analytical calculations that include both diffraction and decoherence effects of characteristics of transition radiation in the THz range were conducted with the input parameters obtained from 3D PIC and hydrodynamic simulations. The calculated characteristics of THz radiation are in good agreement with the experimentally measured ones. Therefore, this approach can be used both to optimize properties of THz radiation and distinguish the transition radiation contribution if several mechanisms of THz radiation generation are considered.