THz Field Induced Second Harmonic Generation in Epsilon Near Zero Indium Tin Oxide Thin Films

Year: 2025

Authors: McDonnell C., Carletti L., Vincenti M.A., Della Valle G., De Angelis C., Celebrano M., Ellenbogen T.

Autors Affiliation: Tel Aviv Univ, Fleischman Fac Engn, Dept Phys Elect, IL-69978 Tel Aviv, Israel; Univ Brescia, Dept Informat Engn, I-25123 Brescia, Italy; Natl Res Council INO CNR, Natl Inst Opt, I-25123 Brescia, Italy; Politecn Milan, Dept Phys, I-20133 Milan, Italy.

Abstract: Epsilon near zero (ENZ) thin films have attracted considerable attention due to their unique optical properties in the near-infrared (NIR), which have enabled a wide range of interesting phenomena and diverse applications. In nonlinear optics, the near-zero permittivity of films in the NIR region has been shown to enhance second-order nonlinear processes by several orders of magnitude, therefore boosting both second harmonic (SH) generation and broadband THz generation. In this work, we investigate THz-field-induced second harmonic (TFISH) generation in indium tin oxide (ITO) thin films in the ENZ spectral region. A symmetry-breaking electric field is applied using a high field strength broadband THz pulse, which when temporally overlapped with an ultrashort optical pulse, results in the emission of second harmonic from the centrosymmetric film. The experimental results mirror very well the predictions of a four-wave mixing optical model, capturing the interplay between linear and nonlinear effects driving the NIR-THz-ITO interaction.

Journal/Review: NANO LETTERS

Volume: 25 (32)      Pages from: 12201  to: 12206

More Information: Tal Ellenbogen acknowledges support from European Union (ERC 3D NOAM 101044797) and Israel Science Foundation (grant No. 1495/23). Michele Celebrano and Luca Carletti acknowledge partial financial support from the European Union’s under Next Generation EU – PNRR – M4C2, investimento 1.1 – PRIN 2022 – NoLimiTHz (id: 2022BC5BW5) CUP D53D23001130006.
KeyWords: Indium tin oxide; Epsilon near zero; THz; Four wave mixing; Second harmonic generation; Nonlinear optics
DOI: 10.1021/acs.nanolett.5c02467