Enhancing second harmonic generation by Q-boosting lossless cavities beyond the time bandwidth limit

Year: 2024

Authors: Franceschini P., Tognazzi A., Chernyak AM., Musorin AI., Cino AC., Fedyanin AA., De Angelis C.

Autors Affiliation: CNR, INO, Via Branze 45, I-25123 Brescia, Italy; Univ Palermo, Dept Engn, Viale Sci Ed 9, I-90128 Palermo, Italy; Univ Brescia, Dept Informat Engn, Via Branze 38, I-25123 Brescia, Italy; Lomonosov Moscow State Univ, Fac Phys, Leninskie Gory 1, Moscow 119991, Russia.

Abstract: Nanostructures proved to be versatile platforms to control the electromagnetic field at subwavelength scale. Indeed, high-quality-factors nanocavities have been used to boost and control nonlinear frequency generation by increasing the light-matter interaction. However, nonlinear processes are triggered by high-intensities, which are provided by ultrashort laser pulses with large bandwidth, which cannot be fully exploited in such devices. Time-varying optical systems allow one to overcome the time-bandwidth limit by modulating the cavity external coupling. Here we present a general treatment, based on coupled mode theory, to describe second harmonic generation in a doubly resonant cavity for which the quality-factor at the fundamental frequency is modulated in time. We identify the initial quality factor maximizing second harmonic efficiency when performing Q-boosting and we predict a theoretical energy conversion efficiency close to unity. Our results have direct impact on the design of next generation time-dependent metasurfaces to boost nonlinear frequency conversion of ultrashort laser pulses.

Journal/Review: NANOPHOTONICS

Volume: 13 (1)      Pages from: 1  to: 8

More Information: The authors acknowledge stimulating discussions with Tal Ellenbogen. A. Tognazzi acknowledges the financial support from the European Union through FESR o FSE, PON Ricerca e Innovazione 2014-2020 – DM 1062/2021 and the University of Palermo through Fondo Finalizzato alla Ricerca di Ateneo 2023 (FFR2023).
KeyWords: time-bandwidth limit; second harmonic generation; time-varying metasurface; Q-boosting
DOI: 10.1515/nanoph-2023-0389


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