Terahertz (THz) imaging is applied to characterize a hybrid fiber-reinforced composite laminate subjected to low-velocity impact in this study. The hybrid fiber-reinforced composite laminate comprises unidirectional glass/epoxy and carbon/epoxy plies with a cross-ply stack pattern, shown in Fig.1. Both impact-induced intra- and inter-laminar damages are successfully detected, and the damage evolution throughout the thickness is also evaluated. The interaction between the THz polarization and carbon-fiber orientation is investigated in detail. Inter-laminar damage at the interface (delamination) and the intra-laminar damage close to the same interface are differentiated via polarization-resolved imaging, as shown in Fig.2. With a parameter fitting method based on multiple regression analysis, delamination is characterized quantitatively. THz C- and B-scan images clearly exhibit the propagation of the damage from the top to the bottom surface in three dimensions
