Enhancing ultrafast nonlinear processes at a nanometer scale has the potential of creating novel nano-sources of energetic photons or particles useful for many applications, especially for embedded diagnostics. In this work, we investigate the plasmonic amplification of the third harmonic generation (THG) from a metal-dielectric-metal (MDM) nano-resonator in the near-terawatt intensity regime. In our geometry, the Fabry-Pérot plasmonic resonator reaches a high local enhancement of the laser electric field over a large volume of a SiO₂ dielectric film. The THG signal is amplified by more than one order of magnitude, with a higher efficiency compared to previous plasmonic geometries. The polarization dependence with respect to the fundamental laser allows an ON/OFF switch of the THG enhancement in the nanostructures which is a strong signature of the plasmonic origin of the THG amplification. Furthermore, the dispersion scan shows that the third harmonic spectrum is strongly redshifted with respect to the peak of its linear extinction spectrum. Using the nonlinear anharmonic model, we confirm that the third harmonic behavior dominantly arises from the silica layer.

增强纳米级的超快非线性过程具有创造高能光子或粒子的新型纳米源的潜力，该纳米源可用于许多应用，尤其是对于嵌入式诊断。在这项工作中，我们研究了金属-电介质-金属（MDM）纳米谐振器在接近兆瓦的强度范围内产生的三次谐波（THG）的等离子体放大。在我们的几何结构中，Fabry-Pérot等离子体共振器在大量SiO _2上实现了激光电场的高度局部增强介电膜。THG信号被放大了一个以上的数量级，与以前的等离激元几何形状相比，效率更高。相对于基本激光器的偏振依赖性允许纳米结构中THG增强的ON / OFF开关，这是THG放大的等离激元起源的有力标志。此外，色散扫描表明，三次谐波频谱相对于其线性消光频谱的峰值发生了强烈的红移。使用非线性非谐模型，我们确认三次谐波行为主要来自二氧化硅层。