Benedetti Alessio, Centini Marco, Bertolotti Mario, Sibilia Concita
Dipartimento di Scienze di Base e Applicate per l'Ingegneria (SBAI), Sapienza Università di Roma, Roma, Italy.
Opt Express. 2011 Dec 19;19(27):26752-67. doi: 10.1364/OE.19.026752.
We numerically study second harmonic generation from dipole gold nanoantennas by analyzing the different contributions of bulk and surface nonlinear terms. We focus our attention to the properties of the emitted field related to the different functional expressions of the two terms. The second harmonic field exhibits different far and near field patterns if both nonlinear contributions are taken into account or if only one of them is considered. This effect persists despite of the model used to estimate the parameters of the nonlinear sources and it is strictly related to the resonant behavior of the plasmonic nanostructure at the fundamental frequency field and to its linear properties at the second harmonic frequency. We show that the excitation of localized surface plasmon polaritons in these structures can remarkably modify the nonlinear response of the system by enhancing surface and/or bulk contributions, creating regimes where bulk nonlinear terms dominate over surface linear terms and vice versa. Finally, the results of our calculations suggest a method that could be implemented to experimentally extract information on the relevance of bulk and surface contributions by measuring and analyzing the generated far field second harmonic patterns in metal nanoantennas and, more in general, in plasmonic nanostructures.
我们通过分析体非线性项和表面非线性项的不同贡献，对偶极金纳米天线的二次谐波产生进行了数值研究。我们将注意力集中在与这两项不同函数表达式相关的发射场特性上。如果同时考虑两个非线性贡献，或者仅考虑其中之一，二次谐波场会呈现出不同的远场和近场模式。尽管用于估计非线性源参数的模型不同，这种效应仍然存在，并且它与等离子体纳米结构在基频场的共振行为及其在二次谐波频率下的线性特性密切相关。我们表明，这些结构中局域表面等离子体激元的激发可以通过增强表面和/或体贡献来显著改变系统的非线性响应，从而产生体非线性项主导表面线性项或反之亦然的情况。最后，我们的计算结果提出了一种方法，该方法可通过测量和分析金属纳米天线以及更一般地在等离子体纳米结构中产生的远场二次谐波模式，来实验提取有关体贡献和表面贡献相关性的信息。
