  Spintronic THz emitters (STE) are efficient THz sources constructed using
thin heavy-metal (HM) and ferromagnetic-metal (FM) layers. To improve the
performance of the STE, different structuring methods (trilayers, stacked
bilayers) have been experimentally applied. A theoretical description of the
overall THz emission process is necessary to optimize the efficiency of STE. In
particular, geometry, composition, pump laser frequency, and spin diffusion
will be significant in understanding the pathways for further research
developments. This work will apply a generalized model based on a modified
Transfer Matrix Method (TMM). We will consider the spin generation and
diffusion in the FM and HM layers and explain the spintronic THz emission
process. This model is suitable for calculating emitted THz signal as a
function of FM and HM thicknesses for different geometrical configurations. We
will investigate a bilayer geometry as a test case, but the extension to a
multi-layer configuration is straightforward. We will show how the different
configurations of the sample will influence the THz emission amplitude.
