Polarization-Independent Enhancement of Third-Harmonic Generation Empowered by Doubly Degenerate Quasi-Bound States in the Continuum.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 39981996.
- Also identified by DOI 10.1021/acs.nanolett.5c00146 and PMC identifier 11887430.
- Licence recorded as CC BY-NC-ND.
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Abstract
Recent advancements in nonlinear nanophotonics are driven by the exploration of sharp resonances within high-index dielectric metasurfaces. In this work, we leverage doubly degenerate quasi-bound states in the continuum (quasi-BICs) to demonstrate the robust enhancement of third-harmonic generation (THG) in silicon metasurfaces. These quasi-BICs are governed by <i>C</i><sub>4<i>v</i></sub> symmetry and therefore can be equally excited with the pump light regardless of polarization. By tailoring the geometric parameters, we effectively control <i>Q</i>-factors and field confinement of quasi-BICs and thus regulate their resonantly enhanced THG process. A maximum THG conversion efficiency up to 1.03 × 10<sup>-5</sup> is recorded under a pump intensity of 5.85 GW/cm<sup>2</sup>. Polarization-independent THG profiles are further confirmed by mapping their signals across the polarization directions. This work establishes foundational strategies for the ultracompact design of robust and high-efficiency photon upconversion systems.