Tailoring terahertz surface plasmon resonances through near-field coupling in multiple holes-based arrays

The phenomenon of extraordinary transmission (EOT) through perforated metal sheets (hole arrays) has been an interesting field of research since its discovery due to its potential applications. In this paper, we focus on the excitation of multiple surface plasmon resonance (SPR) modes in a complex rectangular hole array-based unit cell. This unit cell configuration consists of two horizontally placed holes with a vertical hole placed between them in a near-field electromagnetic coupling regime. We demonstrate, tailoring the SPR resonances along with the Q factor by altering the relative positions among the rectangular holes. Generally, when the excitation field is applied along the longer side of the rectangular hole, no surface plasmon resonance (SPR) is observed. However, in this work, we have shown excitation of SPR modes through near-field interactions even in the case of probe field being applied along the longer side. In such cases, significant modifications in resonance Q-factors are observed which is attributed to near-field interactions among the rectangular holes. Furthermore, our investigation explores the hybridization of (1,0) peaks within the multiple-hole arrays due to the different effective periodicities. Our work also demonstrates a route to excite and tune SPR modes without altering the unit cell periodicity, hence can provide an additional degree of freedom in SPR excitations.