Physics Department, Politecnico di Milano, Piazza Leonardo Da Vinci 32, Milano 20133, Italy.
Nano-Optics &Biophotonics Group - Department of Physics - Experimental Physics 5, University of Würzburg, Am Hubland, Würzburg 97074, Germany.
Nat Nanotechnol. 2015 May;10(5):412-7. doi: 10.1038/nnano.2015.69. Epub 2015 Apr 20.
Boosting nonlinear frequency conversion in extremely confined volumes remains a challenge in nano-optics research, but can enable applications in nanomedicine, photocatalysis and background-free biosensing. To obtain brighter nonlinear nanoscale sources, approaches that enhance the electromagnetic field intensity and counter the lack of phase matching in nanoplasmonic systems are often employed. However, the high degree of symmetry in the crystalline structure of plasmonic materials (metals in particular) and in nanoantenna designs strongly quenches second harmonic generation. Here, we describe doubly-resonant single-crystalline gold nanostructures with no axial symmetry displaying spatial mode overlap at both the excitation and second harmonic wavelengths. The combination of these features allows the attainment of a nonlinear coefficient for second harmonic generation of ∼5 × 10(-10) W(-1), enabling a second harmonic photon yield higher than 3 × 10(6) photons per second. Theoretical estimations point toward the use of our nonlinear plasmonic nanoantennas as efficient platforms for label-free molecular sensing.
在纳米光学研究中，增强极其受限体积内的非线性频率转换仍然是一个挑战，但它可以实现纳米医学、光催化和无背景生物传感等应用。为了获得更亮的非线性纳米级光源，通常采用增强电磁场强度并克服纳米等离子体系统中缺乏相位匹配的方法。然而，等离子体材料（特别是金属）的晶体结构和纳米天线设计的高度对称性强烈抑制了二次谐波的产生。在这里，我们描述了具有非轴对称性的双共振单晶金纳米结构，在激发和二次谐波波长处都具有空间模式重叠。这些特征的结合允许获得二次谐波产生的非线性系数约为 5×10(-10) W(-1)，从而实现每秒超过 3×10(6)个光子的二次谐波光子产率。理论估计表明，我们的非线性等离子体纳米天线可用作无标记分子传感的有效平台。
