Core-cap heterodimer independent of polarization direction of excitation light

Abstract

The plasmonic anisotropic nanostructure possesses the enhanced surface electric field and unique optical properties in near-infrared spectrum, thus it has potential applications in nano-optoelectronics and medical sensing. To obtain the best property, the excitation polarization normally needs to match the orientation of the structure. The strong polarization dependence, however, greatly limits the excitation efficiency. In this work, a patchy structure is introduced to release the dependence of polarization. In the proposed method here in this work, the lost properties due to unmatched polarizations are compensated for by the plasmonic resonance coupling between the patch and capped structure in the heterozygous dimer. By overlapping the two modes at the same wavelength, the absorption keeps rather stable undisturbed status during the variation of incident polarization. This work focuses on the theoretical exploration of the feasibility. Electromagnetic field in the interaction between light and heterozygous dimer is essential before extinction coefficient is calculated. The field of the model is obtained by solving Maxwell equations through using the finite element method. The numerical calculation presents a good understanding of the mechanism of the plasmonic interactions in the dimer, based on which the nanostructure with optimized configuration parameters can achieve the stable and high absorption in the near infrared wavelength.