THz transition radiation of electron bunches 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 µC). This regime could be of interest for high-energy THz radiation generation, as many of the mechanisms have a scaling ∝Q2 . In this work, we focus specifically on the challenges that arise during numerical investigations of transition radiation in such interactions. Detailed analytical calculations that include both the diffraction and decoherence effects of the characteristics of transition radiation in the THz range were conducted with the input parameters obtained from 3D particle-in-cell 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 the properties of THz radiation and to distinguish the transition radiation contribution if several mechanisms of THz radiation generation are considered.