The optimization of nonlinear optical processes at the nanoscale is a key challenge in nanoscience. In this framework, plasmon-enhanced nonlinear effects together with the development of innovative nanoantenna designs and hybrid nanostructures are receiving a lot of attention [1-2]. We recently devised a plasmonic nanoantenna working in the near-infrared region of the electromagnetic spectrum, which allows boosting the SHG efficiency. This is achieved by optimizing the nanoantenna geometry to feature (i) a double resonant response at both the excitation and emission wavelengths, (ii) a spatial overlap between the modes involved in the process and (iii) a broken symmetry, to enable dipole-allowed SHG. We found that this nanoantenna behaves like a strongly coherent nanoscale light source, featuring a marked THG along with an intense SHG [3-4].
We find evidence of a SHG-mediated cascaded effect in THG . We have identified a THG polarization behavior that strongly deviates from that of a bulk (3)-mediated effect and unveils a significant contribution coming from the cascaded coherent sum of a SHG photon and a pump photon.
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Costantino De Angelis, Michele Celebrano, Lavinia Ghirardini, Giovanni Pellegrini, Paolo Biagioni, Xiaofei Wu, Swen Grossmann, Luca Carletti, Andrea Locatelli, Lamberto Duò, Bert Hecht, and Marco Finazzi, "Competing second and third order nonlinear effects in plasmonic nanoantennas (Conference Presentation)," Proc. SPIE 10540, Quantum Sensing and Nano Electronics and Photonics XV, 105400U (Presented at SPIE OPTO: January 30, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2288377.5751530976001.
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