Fig. 4. Evidence for confirming the effect of strong coupling and the proposed model.

a Transferred hot electron densities and corresponding η for the heterostructure with a 700 nm grating period at different pump wavelengths. b Branches of Ψ₂ (|c₂₁|², |c₂₂|², and |c₂₃|²) as a function of the grating period. c The simulated absorbance of the heterostructures with grating periods of 600, 650, 700, and 750 nm. For a grating period of 700 nm, the absorbance is approximately 0.4 when Ψ₂ is resonantly excited. d A diagrammatic model proposed to describe the physical processes in the strong coupling regime between LSPs and surface plasmon polaritons. Coherent energy exchange is represented by the dashed lines labeled by ① and ②. The processes labeled as ③ and ④ denote the radiative and nonradiative relaxation channels of the LSPs, respectively. LSP localized surface plasmon