Impact of plasmonic substrate of different geometries on the enhancement factor of hyper‐Raman scattering process

Abstract

Effective plasmonic heterotrimers of different geometry have been proposed as an active substrate to substantially enhance the scattered signal of hyper-Raman scattering process. The three-particle systems are constructed independently from asymmetric nanoparticles of spherical, cylindrical, and spheroidal shapes. The interacting metallic characters in each one of the three trimers are arranged collinearly in a J-aggregate configuration and illuminated by a longitudinally polarized light. The finite-difference time-domain electrodynamic simulation tool is employed to simulate optical cross-section and nearfield intensity associated with the excited plasmonic bands. The extinction profile of each one of the three trimers exhibits the excitation of two plasmonic modes. The first is a superradiant mode, which resulted from the in-phase coupling between the dipole moments induced in each one of the three plasmonic elements. The second mode excited at a shorter wavelength, which is a combination between bright and dark modes (Fano interference). The resonance wavelength of the former mode matches the incident one; meanwhile, the resonance energy of the Fano profile is equivalent to the second-order Stokes condition. From the values of the highly enhanced nearfield associated with the observation of these modes, the enhancement factor of the hyper-Raman scattering process is calculated. The simulation results highlight the influence of the selected particle's geometry on both the quality of plasmonic coupling and calculated enhancement factor. The maximum value of the enhancement factor can reach as high as 3.83 × 1017 when the heterotrimer is constructed from spheroids. For nanoparticles of spherical shape, the calculated value of the factor is comparable to the maximum limit; meanwhile, the rod shape demonstrates the minimum limit of the enhancement factor.