Nonlinear THz Generation through Optical Rectification Enhanced by Phonon-Polaritons in Lithium Niobate Thin Films

Year: 2023

Authors: Carletti L., Mcdonnell C., Leon UA., Rocco D., Finazzi M., Toma A., Ellenbogen T., Della Valle G., Celebrano M., De Angelis C.

Autors Affiliation: Univ Brescia, Dept Informat Engn, I-25123 Brescia, Italy; Natl Res Council INO CNR, Natl Inst Opt, I-25123 Brescia, Italy; Tel Aviv Univ, Fleischman Fac Engn, Dept Phys Elect, IL-69978 Tel Aviv, Israel; Politecn Milan, Dept Phys, I-20133 Milan, Italy; Ist Italiano Tecnol, I-16163 Genoa, Italy.

Abstract: We investigate nonlinear THz generation from lithium niobate films and crystals of different thicknesses by optical rectification of near-infrared femtosecond pulses. A comparison between numerical studies and polarization-resolved measurements of the generated THz signal reveals a 2 orders of magnitude enhancement in the nonlinear response compared to optical frequencies. We show that this enhancement is due to optical phonon modes at 4.5 and 7.45 THz and is most pronounced for films thinner than 2 mu m where optical-to-THz conversion is not limited by self-absorption. These results shed new light on the employment of thin film lithium niobate platforms for the development of new integrated broadband THz emitters and detectors. This may also open the door for further control (e.g., polarization, directivity, and spectral selectivity) of the process in nanophotonic structures, such as nanowires and metasurfaces, realized in the thin film platform. We illustrate this potential by numerically investigating optical-to-THz conversion driven by localized surface phonon-polariton resonances in sub-wavelength lithium niobate rods.

Journal/Review: ACS PHOTONICS

Volume: 10 (9)      Pages from: 3419  to: 3425

More Information: This work was supported by Ministero dell’Istruzione, dell’Universita e della Ricerca (2017 MP7F8F, PRIN NOMEN; 2020EY2LJT_002, PRIN METEOR); European Union (ERC 3D NOAM 101044797); European Commission (899673, FETOPEN-01-2018-2019-2020).
KeyWords: lithium niobate; THz generation; optical rectification; THz phonons; phonon-polaritons; localized surfacephonon-polaritons
DOI: 10.1021/acsphotonics.3c00924

Citations: 12
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