Further localization of optical field for flower-like silver particles under laser radiation

We find the surface optical field of submicron silver particles can be further localized by their surface roughening, which leads to a greatly enhanced local field. The flower-like silver particles were prepared and the extinction spectra were measured in our work. A high enhancement factor of 1.3 × 107 was obtained by surface-enhanced Raman spectrum. Besides that, the correlation between the surface plasmon resonance mode and surface local field was also studied by theoretical analysis. The results show the plasmon resonance modes of flower-like silver particles include dipole and multipole plasmon resonances. For the dipole plasmon resonance at long wavelength, the local field near polar regions will be further localized as a result of the rough surface. In contrast, the interaction of local field between surface structures will cause hotspots for the multipole plasmon resonance in the short-wave region. Based on these factors, we demonstrate that the rough-surface-induced field superposition results in the redistribution and enhancement of the optical field around the particles. (letter)