Manipulating light–matter interaction in a gold nanorod assembly by plasmonic coupling

P A P ER Abstract The interaction of light with a single gold nanorod (GNR) depends strongly on the polarization and wavelength of the light. For isolated GNRs, the maximum of the polarization (wavelength)-dependent linear and nonlinear absorption appear at the same excitation polarization (wavelength). Here, it is demonstrated that these relationships can be manipulated in a GNR assembly composed of randomly distributed and oriented GNRs by controlling the plasmonic coupling strength between GNRs. It is revealed that the strongly localized modes resulting from the plasmonic coupling of GNRs play a crucial role in determining these relationships. For a GNR tetramer, it is shown by numerical simulation that the maximum two-photon absorption achieved at a particular polarization can be switched to theminimumabsorption and vice versa by controlling the coupling strength. More importantly, it is demonstrated both numerically and experimentally that the two-photon-absorption peak of a GNR assembly can be made to be different from its singlephoton-absorption peak by increasing the coupling strength. Both properties are distinct from previous experimental observations. Our findings provide a useful guideline for engineering the interaction of light with complex plasmonic systems.