Point-by-point near-field optical energy deposition around plasmonic nanospheres in absorbing media

Abstract

Here we investigate the effects of absorbing media on plasmon-enhanced near-field optical energy deposition. We find that increasing absorption by the medium results in increased particle scattering at the expense of particle absorption, and that much of this increased particle scattering is absorbed by the medium close to the particle surface. We present an analytical method for evaluating the spatial distribution of near-field enhanced absorption surrounding plasmonic metal nanospheres in absorbing media using a new point-by-point method. We propose criteria to define relevant near-field boundaries and calculate the properties of the local absorption enhancement, which redistributes absorption to the near-field and decays asymptotically as a function of the distance from the particle to background levels. Using this method, we performed a large-scale parametric study to understand the effect of particle size and wavelength on the near-field absorption for gold nanoparticles in aqueous media and silicon, and identified conditions that are relevant to enhanced local infrared absorption in silicon. The presented approach provides insight into the local energy transfer around plasmonic nanoparticles for predicting near-field effects for advanced concepts in optical sensing, thin-film solar cells, nonlinear imaging, and photochemical applications.

Phase function of a spherical particle when scattering an inhomogeneous electromagnetic plane wave

“…Scattering of an inhomogeneous wave by a particle in a nonabsorbing medium [18] is useful in total internal reflection microscopy [19], as this is based on the scattering by particles of an evanescent wave. Scattering by particles in absorbing media has especially received attention in random lasing [29][30][31][32] and solar cell absorption enhancement [33][34][35][36][37]. In the former area, the laser gain medium is often a dye solution with embedded particles, and researchers investigate the influence of scattering on the output character of the laser.…”