The Double-resonance Enhancement of Stimulated Low-Frequency Raman Scattering in Silver-capped Nanodiamonds

摘要

Hybrid plasmonic-dielectric nano- and (sub)microparticles exhibit magnetic and electrical dipolar Mieresonances, which makes them useful as efficient basic elements in surface-enhanced spectroscopy, non-linear light conversion and nanoscale light control. We report the stimulated low-frequency Raman scattering (SLFRS) of a nanosecond ruby laser radiation (central wavelength λ= 694.3 nm (full-width at half-maximum ≈ 0.015 cm~(-1)), gaussian 1/e-intensity pulsewidth τ ≈ 20 ns, TEM_(00)-mode pulse energy E_(max) ≈ 0.3 J) in nanodiamond (R ≈ 120 nm) hydrosols, induced via optomechanical coherent excitation of fundamental breathing eigen-modes, and the two-fold enhancement of SLFRS in Ag-decorated nanodiamonds, characterized by hybrid dipolar resonances of electrical (silver) and magnetic (diamond) nature. Hybrid metal-dielectric particles were prepared by means of nanosecond IR-laser ablation of solid silver target in diamond hydrosols with consecutive Ag-capping of diamonds, and were characterized by scanning electron microscopy, UV-vis, photoluminescence and energy-dispersive X-ray spectroscopy. Intensities of the SLFR-scattered components and their size-dependent spectral shifts were measured in the highly sensitive stimulated scattering regime, indicating the high (≈ 30%) SLFRS conversion efficiency and the resonant character of the scattering species.