Phase-Matched Second-Harmonic Generation from Metasurfaces Inside Multipass Cells Madona Mekhael, Timo Stolt, Anna Vesala, Heikki Rekola, Tommi K. Hakala, Robert Fickler and Mikko J. Huttunen EPJ Web Conf., 309 (2024) 08006 Published online: 31 October 2024 DOI: 10.1051/epjconf/202430908006