Plasmon-enhanced depolarization of reflected light from arrays of nanoparticle dimers.

Using spectroscopic ellipsometry and analytical multiple scattering theory, we demonstrate significant depolarization of far-field reflected light due to plasmonic near-field concentration in dimer arrays of metallic nanoparticles fabricated by electron beam lithography. By systematically investigating dimer arrays with varying sub-wavelength interparticle separations, we show that the measured depolarization presents a sharp peak at the Rayleigh cutoff condition for efficient in-plane diffraction. Moreover, by investigating the depolarization of reflected light as a function of the excitation angle, we demonstrate that maximum depolarization occurs in the spectral regions of plasmon-enhanced near-fields. Our results demonstrate that far-field reflection measurements encode information on the near-field spectra of complex nanoparticle arrays, and can be utilized to experimentally determine the optimal conditions for the excitation of sub-wavelength plasmonic resonances. The proposed approach opens novel opportunities for the engineering of nanoparticle arrays with optimized enhancement of optical cross sections for spectroscopic and sensing applications.