Spectroscopic amplifier for ultrahigh plasmonic-based enhancement of the hyper-Raman scattering procedure

An anisotropic plasmonic trimer is proposed as an effective spectroscopic amplifier for the maximum signal enhancement of the hyper-Raman Scattering (HRS) process. The three-particle system is composed of asymmetric Au nanorings arranged collinearly in a J-aggregate configuration and illuminated by a longitudinally polarized light. The optical properties of the considered trimer have been numerically simulated by the finite-difference time-domain method. The extinction profile of the heterotrimer exhibits the excitation of two plasmonic bands, superradiant and subradiant (Fano interference) modes. From the associated highly enhanced and strongly localized nearfield, the enhancement factor of the surface-enhanced HRS (EF_SEHRS) is calculated. The simulation results demonstrate the impact of both the thickness and height of the interacting rings on the Raman factor. To reach the desired value of the EF_SEHRS, the thickness of the rings should be maximized, and their height must be minimized. These two factors work together to enormously increase the charge density accumulated in the intercoupling region, the associated nearfield intensity, and therefore significantly augment the corresponding EF_SEHRS. The EF_SEHRSincreases exponentially with decreasing height and increasing thickness of the trimer system. For selected values of both thickness and height, EF_SEHRScan reach a value never reported before, as high as 5.6 × 10²³.