Layer-resolved pump absorptance in spintronic/orbitronic terahertz emission modeling: A transfer matrix Poynting flux analysis method with sample-specific parameter fittings

Abstract

Quantitative interpretation of thickness-dependent spintronic/orbitronic terahertz (THz) emitter (STE/OTE) experiments requires reliable knowledge of how pump energy is distributed among individual layers. However, this distribution is often approximated using tabulated optical constants or simple thickness-weighted estimation, which may not represent actual thin-film spectral parameters. Here, we develop a sample-specific optical-analysis workflow based on transfer-matrix modeling combined with Poynting-flux evaluation. The workflow supports forward calculation and thickness-dependent modeling with retrieval of effective optical constants. Using representative Sub/Pt/NiFe, Sub/W/NiFe, and Sub/Ta/NiFe series, we show that thickness-dependent reflectance, transmittance, and absorptance data can be self-consistently reproduced using a single set of effective optical constants for the varying layer, from which layer-resolved pump absorptance is obtained. Comparison with thickness-weighted partitioning further shows that, although simple rules may capture qualitative trends, rigorous sample-specific investigation provides a more reliable description of pump-energy deposition for quantitative STE/OTE analysis.