Work

Observation of surface frequency doubling in Si(111) mediated by a $$\chi ^4$$ process

Year: 2026

Type: article

Abstract: Nonlinear optical processes such as second-harmonic generation (SHG) provide powerful probes of the structural and electronic properties of semiconductor surfaces and interfaces. While SHG in centrosymmetric materials like silicon has been extensively investigated, higher-order nonlinear contributions remain largely unexplored. Here, we report for the first time the observation of a $$\chi ^4$$ -mediated contribution to SHG from Si(111)– $$SiO_2$$ interfaces, revealed through intensity scaling and azimuthal anisotropy measurements. The frequency-doubled signal exhibits both quadratic and quartic dependence on the incident intensity, with the quartic term displaying a distinct threefold symmetry superimposed on the conventional sixfold SHG pattern. This identifies a previously unreported pathway for nonlinear emission at silicon surfaces. These results were enabled by high-intensity excitation near the laser-induced damage threshold, combined with automated high-sensitivity detection.

Source: Scientific Reports

DOI: 10.1038/s41598-026-70079-3

Authors: H. Pires, H. Gomes, C. Priebe, G. Figueira, A. Silva

Institutions: University of Lisbon, Instituto Superior Técnico, Technical University of Applied Sciences Lübeck, University of Lübeck, Universidade Nova de Lisboa

Language: English

Topic: Photorefractive and Nonlinear Optics

Subfield: Atomic and Molecular Physics, and Optics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,690

OpenAlex ID: W7225791412

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