ナノ金粒子の集まりに励起される局在プラズモン

摘要

複数個のナノ金属粒子による光の散乱問題をGMTにより数値解析し，局在プラズモン（dipolar plasmons）について多重極展開（ベクトル波動関数の展開係数）から調べた．そして，下記の事を確認した：（1）局在プラズモンが励起するところで多重極展開のn＝1次のモードが共振している；（2）このモードは，入射光の偏光方向に双極子を形成し，電場増強を起こす；（3）局在プラズモンが励起しているナノ金粒子を近づけると双極子の相互作用により，n＝2次のモードで共振が生じる；（4）近接するナノ金粒子に励起する局在プラズモンは，粒子間の局在した領域で電場増強を生じる．%Absorption and scattering of visible light by a cluster of nano-sized gold particles is numerically analysed in connection with localized surface plasmons. The numerical technique employed here is based on the Generalized Multipole Technique (GMT) in which the fields inside and outside the particles are expanded in spherical vector wave functions. We first confirm the dipolar plasmon resonance in a nano-sized gold particle: the expansion coefficients of the 1st-order spherical mode exhibit the characteristic of resonance when the localized surface plasmon mode is excited on a nanoparticle. Next, we investigate the interaction between the surface plasmon modes excited on each particle of a cluster of nano-sized gold particles. It is confirmed that the interaction has large influence on the localization and enhancement of the near field of a cluster of nano-sized metal particles.