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. (C) 2011 Optical Society of America