Controlling Plasmonic Field Enhancement via the Interference of Orthogonal Plasmonic Modes

Optical nanoantennas concentrate light into their local fields. The field concentration property is governed by the plasmonic resonances and their interference. Here, we present a method for controllable local-field interferences in the hot spot of nanorods and experimentally demonstrate that the field enhancement can be tuned in a wide range. For this, we design nanoparticles with given phase relations between their plasmonic eigenmodes and at the same time tune the phase between the components of the external field by changing its polarization state to achieve in-phase excitation of the plasmon modes. Strong-field photoemission is applied to probe the field enhancement property of the nanorods employing femtosecond pulses of different polarization states. Our findings provide a new degree of freedom in plasmonic resonance tuning and may inspire diverse designs of local-field responses and expand the applications in nanoscale sensing, spectroscopy, and dynamically tunable devices.