Second harmonic generation at a time-varying interface

Romain Tirole; Stefano Vezzoli; Dhruv Saxena; Shu Yang; T V Raziman; Emanuele Galiffi; Stefan A Maier; John B Pendry; Riccardo Sapienza

doi:10.1038/s41467-024-51588-z

Second harmonic generation at a time-varying interface

Nat Commun. 2024 Sep 5;15(1):7752. doi: 10.1038/s41467-024-51588-z.

Authors

Romain Tirole¹, Stefano Vezzoli², Dhruv Saxena², Shu Yang², T V Raziman², Emanuele Galiffi³, Stefan A Maier^{2

4}, John B Pendry², Riccardo Sapienza⁵

Affiliations

¹ Blackett Laboratory, Department of Physics, Imperial College London, London, SW7 2BW, UK. romain.tirole13@gc.cuny.edu.
² Blackett Laboratory, Department of Physics, Imperial College London, London, SW7 2BW, UK.
³ Photonics Initiative, Advanced Science Research Center, City University of New York, 85 St. Nicholas Terrace, 10031, New York, NY, USA.
⁴ School of Physics and Astronomy, Monash University, Clayton, VIC, 3800, Australia.
⁵ Blackett Laboratory, Department of Physics, Imperial College London, London, SW7 2BW, UK. r.sapienza@imperial.ac.uk.

Abstract

Time-varying metamaterials rely on large and fast changes of the linear permittivity. Beyond the linear terms, however, the effect of a non-perturbative modulation of the medium on harmonic generation remains largely unexplored. In this work, we study second harmonic generation at an optically pumped time-varying interface between air and a 310 nm Indium Tin Oxide film. We observe a modulation contrast at the second harmonic wavelength up to 93% for a pump intensity of 100 GW/cm², leading to large frequency broadening and shift. We experimentally demonstrate that a significant contribution to the enhancement comes from the temporal modulation of the second order nonlinear susceptibility. Moreover, we show the frequency-modulated spectra resulting from single and double-slit time diffraction could be exploited for enhanced optical computing and sensing, enabling broadband time-varying effects on the harmonic signal and extending the application of Epsilon-Near-Zero materials to the visible range.