Efficient Third Harmonic Generation in All-dielectric and Dielectric-metallic Nanoantennas Excited at Anapole Modes

G. GRINBLAT; Y. LI; T. SHIBANUMA; M. P. NIELSEN; P. ALBELLA; R. F. OULTON; S. A. MAIER

Simposio; Progress In Electromagnetics Research Symposium; 2017

The quest for nanomaterials delivering efficient harmonic generation in the optical regime has progressed significantly in recent years.[1,2] In particular, one of the most promising approaches for third harmonic generation (THG) at subwavelength volumes consists of engineering high permittivity materials to produce optical nanoantennas capable of efficiently concentrating light at the fundamental frequency inside them.[3-6] Indeed, this strategy not only delivers an effectively increased pump intensity, boosting the nonlinear effect, but also, due to Miller´s rule, provides large intrinsic third-order nonlinear susceptibilities (chi(3)) as utilizes high permittivity materials. In this context, high-refractive-index dielectrics are promising candidates for producing strong nonlinear phenomena due to both field confinement effects and high chi(3) values. In this presentation, the single germanium nanodisk, with a refractive index greater than 4, is introduced as a new and simple system for producing efficient THG at 550 nm.[5,6] It is found that the highest emission occurs when the nanodisk is excited near anapole modes, where the coupling to the far-field is minimum and the electric field within the dielectric is maximum, as shown by numerical simulations consistent with the measured extinction spectra. Under these conditions, the germanium nanodisk is found to present third harmonic conversion efficiencies as large as 0.001%, with an associated enhancement of 4 orders of magnitude with respect to the bulk.In this investigation, it is also demonstrated that the measured wavelength dependence of the third harmonic signal intensity serves as an excellent method to probe relative values of the electric energy stored within the dielectric nanoantenna.[5,6] In addition, by mapping the THG emission across the nanodisk, the anapole near-field intensity distributions are unveiled, showing excellent agreement with numerical simulations. Finally, it is revealed that the nonlinear performance can be further improved, throughout the whole visible regime, by developing hybrid dielectric/metallic (silicon/gold) nanoantennas.[7] The results presented in this work deepen the understanding on THG processes through resonant modes in dielectric-based nanostructures, and pave the way towards novel alternatives for highly-efficient infrared-to-visible light conversion devices in the nanoscale.[1] Grinblat, G.; Rahmani, M.; Cortés, E.; Caldarola, M.; Comedi, D.; Maier, S. A.; Bragas, A. V. Nano Lett. 2014, 14, 6660-6665.[2] Aouani, H.; Rahmani, M.; Navarro-Cía, M.; Maier, S. A. Nat. Nanotech. 2014, 9, 290-294.[3] Shcherbakov, M. R.; Neshev, D. N.; Hopkins, B.; Shorokhov, A. S.; Staude, I.; Melik-Gaykazyan, E. V.; Decker, M.; Ezhov, A. A.; Miroshnichenko, A. E.; Brener, I.; Fedyanin, A. A, Y. S. Kivshar. Nano Lett. 2014, 14, 6488-6492.[4] Shorokhov, A. S.; Melik-Gaykazyan, E. V.; Smirnova, D. A.; Hopkins, B.; Chong, K. E.; Choi, D. Y.; Shcherbakov, M. R.; Miroshnichenko, A. E.; Neshev, D. N.; Fedyanin, A. A.; Kivshar, Y. S. Nano Lett. 2016, 16, 4857-4861.[5] Grinblat, G.; Li, Y.; Nielsen, M., Oulton R. F.; Maier S. A. Nano Lett. 2016, 16, 4635-4640.[6] Grinblat, G.; Li, Y.; Nielsen, M., Oulton R. F.; Maier S. A. ACS Nano 2017, DOI: 10.1021/acsnano.6b07568.[7] Shibanuma, T.; Grinblat, G.; Albella, P.; Maier S. A. Submitted, 2017.