Unai Arregui Leon, former EMIMEP student (Politecnico di Milano – EMIMEP Associated partner) delivered a conference entitled « Modeling strategies for THz nonlinear nanophotonics enabled by all-dielectric metastructures » at the University of the Basque Country (Spain) during our 2025 Summer School on August 27th, 2025.

Abstract. Historically, the THz region of the electromagnetic spectrum is one of the less explored windows due to the limitations inherently associated with such a spectral range (high material and atmospheric absorption, lack of powerful and tunable table-top sources, etc). After the success proved by sub-wavelength metallic nanostructures to localize and
enhance near-infrared and visibile light, dielectric nanoantennas have been proposed as promising candidates to translate such a potential down to the THz, specially in the nonlinear regime. As such, the first half of the presentation aims at showing how the optical rectification of a near-infrared signal held in an isolated all-dielectric nanoscatterer can be numerically modeled, by resorting to semi-analytical approaches for understanding the farfield characteristics of the nonlinearly emitted THz signal (radiation pattern, conversion
e^iciency…). On the other side, the second half of the seminar will deal with the extension of the problem to two-dimensional periodic arrangements of the aforementioned dielectric nanoantennas. The computational method developed for simulating the di^erencefrequency generation process in phonon-polaritonic metasurfaces will be presented, and the way in which this approach can be exploited for tackling applications in the field of nonlinear THz light generation and manipulation will be reported, including all-optical modulation in spatial and temporal domains.

Bio. Unai was born in Tolosa (Basque Country, Spain) in 1996. He obtained the BSc Degree in Physics and the BSc Degree in Electronic Engineering both at the Faculty of Science and Technology of the University of the Basque Country (UPV/EHU) in 2019. Between 2019 and 2021, he was awarded an Erasmus Mundus Scholarship to pursue the Joint Master Degree on Innovative Microwave Electronics and Optics (EMIMEO) at the University of Limoges (France), University of Brescia (Italy) and the UPV/EHU. After obtaining the mentioned MSc Degree, on November 2021 he joined the Computational Electromagnetics Lab of the Department of Physics of Politecnico di Milano (Italy) to pursue his PhD studies under the supervision of Prof. Giuseppe Della Valle, focusing on the modeling and design of nonlinear all-dielectric metastructures for THz nanophotonics. From August 2024 to December 2024, he was a visiting PhD researcher at the Lattice Dynamics Group in the Physical Chemistry Department of the Fritz Haber Institute of the Max Planck Society in Berlin (Germany). Unai obtained the PhD title in Physics (Cum Laude) on March 2025, and he is currently a Research and Teaching Assistant at the Department of Physics of Politecnico di Milano.