Abstract
Plasmonic dark modes are pure near-field resonances since their dipole moments are vanishing in far field. These modes are particularly interesting to enhance nonlinear light-matter interaction at the nanometer scale because radiative losses are mitigated therefore increasing the intrinsic lifetime of the resonances. However, the excitation of dark modes by standard far field approaches is generally inefficient because the symmetry of the electromagnetic near-field distribution has a poor overlap with the excitation field. Here, we demonstrate the selective optical excitation of bright and dark plasmonic modes of single gold nanorods by spatial phase-shaping the excitation beam. Using two-photon luminescence measurements, we unambiguously identify the symmetry and the order of the emitting modes and analyze their angular distribution by Fourier-space imaging.
Highlights
Localized surface plasmons (LSPs) are quantized collective oscillations of conduction electrons sustained by metal nanoparticles
Because two-photon luminescence non linear process (TPL) intensity has a quadratic dependence on the near-field intensity an increase signal relates to a local enhancement of the electric field; TPL measurements are an efficient tool to identify LSP resonances [17]
In order to reduce the impact of this field enhancement compared to the exaltation due to surface plasmon resonances, we report here the mean electric field intensity integrated in a volume of 5 nm around the nanorods instead of its maximum
Summary
Localized surface plasmons (LSPs) are quantized collective oscillations of conduction electrons sustained by metal nanoparticles. J. Garca de Abajo, “Probing bright and dark surface-plasmon modes in individual and coupled noble metal nanoparticles using an electron beam,” Nano Letters 9, 399–404 (2009).
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