posted on 2024-03-13, 12:40authored byShijia He, Yi Wang, Tianyu Wang, Dongda Wu, Junqiao La, Jiang Hu, Yan Zheng, Fanzhou Lv, Yudie Huang, Wenxin Wang
We report a strategy for preparing cost-effective plasmonic
square
lattices with tunable unit structures of circles, crosses, and circle-cross
pairs on a centimeter scale. The asymmetrical electromagnetic (EM)
field distribution of the lattice enhances second harmonic generation
(SHG) under oblique incidence. The SHG signals are progressively strengthened
as the unit symmetry decreases from C∞v (circle) to C4v (cross) to C2v (circle-cross pair). The peak SHG signal is observed from the plasmonic
lattice with a circle-cross pair, showcasing a conversion efficiency
of 1.0 × 10–2, which is a 7.3-fold enhancement
relative to the dielectric lattice comprised of circle units. This
notably high conversion efficiency of SHG is on par with that of phase-matched
bulk nanostructures under normal incidence, benefiting from the Bloch-surface
plasmon polariton (Bloch-SPP) modes associated with the distribution
of the photonic local density of states (LDOS). Furthermore, the SHG
emission exhibits distinctive directional and polarization characteristics
as the unit symmetry is reduced. This work offers valuable insights
into a structural symmetry-dependent SHG in plasmonic lattices and
the way forward for the design of functional nonlinear plasmonic devices.