PNNL

Abstract

The role of surface plasmon polaritons (SPPs) in nanohole array optical extinction spectra is explored using a time-resolved technique capable of isolating the air/metal interfacial SPP contribution to the typical Fano profile in optical transmission curves. A pair of interferometrically-locked broad-band femtosecond pulses is used to launch SPPs from lithographically patterned plasmonic nanohole arrays. SPPs launched in the forward and backward propagation direction are probed using a third probe pulse in a photoemission electron microscope (PEEM). Using this approach, we record interferometric SPP-SPP autocorrelations that selectively report on the resonances of SPPs launched from arrays of varying pitch and hole diameter. Besides advancing a novel approach to selective SPP spectroscopy, we illustrate that resonant coupling in the backward propagating direction may be exploited to control the spatial, temporal, and spectral characteristics of SPPs. For the counter-propagating direction, we show that tuning the array pitch near the fundamental plasmon resonance generates color-tuned (~770-820 nm), narrow bandwidth SPPs and that the bandwidth may be controlled by changing the ratio of pitch to hole diameter. The SPP resonances we recover through Fourier transforms of the interferometric autocorrelations shed light on the classical problem of Fano interference in nanohole array extinction spectra.