  Direct laser electron acceleration in near-critical density plasma produces
collimated electron beams with high charge $Q$ (up to $\mu$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.
