Prof. Giuseppe Leo (Laboratoire Matériaux et Phénomènes Quantiques, Université Paris Cité and CNRS, France) provided a seminar at the University of Brescia on Friday 05 July 2024 entitled « Nonlinear generation of structured light with metasurfaces and thin films ».

Abstract. The generation of structured light dates back to Young’s double-slit interference experiment, and for a long time it has been related to the linear superposition of wave fronts. After the broad development of spatial light modulators a few decades ago, this paradigm has been reconducted by the advent of optical metasurfaces. However, the potential of light structuring is even stronger and more fascinating in the nonlinear regime, where the present maturity of nonlinear meta-optics enables to create light harmonics with unprecedented phase, amplitude, polarization and topological complexity. Within this fascinating research field, the generation of vortex beams has become an interesting test bed for design and experimental protocols, because of their relevance in both fundamental and applied physics. Here, we report on our recent results on the generation of second-harmonic vortices with either a uniform dielectric film or an optical metasurface. In the former case we demonstrate spin-to-orbital angular momentum mediated by the nonzero electric-field longitudinal component of the pump beam, while in the latter we generate high-purity orbital angular momentum with an arbitrary topological charge via a nonlinear meta-hologram. Both results are achieved in AlGaAs-on-insulator platforms. 

Biography. Prof. Giuseppe Leo (born in Italy in 1966) received a Laurea degree (cum laude) in Electronic Engineering at La Sapienza, Rome (1990), and a PhD in Physics at Paris-Saclay University (2001). He has been with Roma Tre University as assistant (1992-2002) and associate professor (2002-04), as well as visiting scientist at CSELT (1994-95) and Thomson-CSF (1998). Since 2004 he has been full professor at Université Paris Cité, where he founded and directed the Denis Diderot School of Engineering (2010-22) and has led the Nonlinear Optical Devices group of MPQ since 2007. His research is in nonlinear integrated optics, nanophotonics and metasurfaces. Optica Fellow since 2020 and Member of Institut Universitaire de France since 2023, he coordinates and/or participates in several national and EU research programs. Prof. Leo served as co-chair in SPIE Photonics West and Optica MICS, co-organized several more conferences, and is member of the Université Franco-Italienne and the editorial board of Opto-Electronic Advances. He published 141 articles, 2 books, 13 book chapters, he registered 4 patents, and he gave 102 invited conferences (with 5 keynote) and 45 invited seminars in several institutions. According to Google Scholar, he got 5261 citations and h-41.