Gold-polymer hybrid metasurface for polarization-independent enhanced third harmonic generation in the ultraviolet

TL;DR

This work tackles polarization dependence in metasurface nonlinear optics by introducing a quasi-3D gold–polymer hybrid metasurface that supports both TE and TM modes. The authors combine a hexagonal SU8 nanohole/gold structure with full-field 3D simulations and ultrafast THG measurements to achieve polarization-independent upconversion into the UV. They report resonant THG near 790 nm with enhancement factors up to about 400 when diffracted orders are included, validated by experiment and modeling. The results point to a scalable route for compact, polarization-agnostic UV sources and open pathways for integrated nano-photonic devices in spectroscopy, sensing, and quantum photonics.

Abstract

We present a combined experimental and theoretical study of nonlinear light-matter interactions in a three-dimensional gold-polymer hybrid metasurface. In contrast to conventional two-dimensional designs, which by symmetry may support either transverse electric (TE) or transverse magnetic (TM) polarization, our volumetric architecture accepts both TE and TM modes simultaneously, reflecting the dimensionality and versatility required by the photonic devices. The metasurface comprises a periodic lattice of gold nanostructures embedded in a dielectric polymer matrix, creating complex metal-dielectric interfaces that sustain tightly confined plasmonic resonances. When driven by ultrafast near-infrared pulses, these resonances concentrate optical energy at the nanoscale, enabling efficient third-harmonic generation and upconversion of visible light into the ultraviolet (UV) and deep-UV regimes with enhanced conversion efficiency. We perform spatial and temporal mapping of the nonlinear response under both TE and TM excitation. Our measurements reveal polarization-agnostic field enhancement and spectral tunability arising from the three-dimensional morphology-capabilities unattainable in planar metasurfaces, where two-dimensional symmetry inherently limits polarization flexibility and functional bandwidth. This 3D platform provides a flexible design toolbox for polarization-independent UV and deep-UV light sources. Potential applications include high-resolution UV spectroscopy, optical multiplexing, data storage, and emerging quantum photonic architectures. By establishing fundamental insights into three-dimensional nonlinear metasurface behavior, our work paves the way for next-generation reconfigurable, multi-polarization nanophotonic devices.

Figures (8)

• Figure 1: Sample schematic representation (a) 3D view of the quasi-3D hybrid structure, with the following dimensions $p=800 nm, h_{Au}=50 nm, d=367 nm$, and $h_{SU8}=390 nm$ (b) zoom in side view displaying the two layers of periodicity i.e. the upper layer of thin gold film with a nanohole array and the underlying gold nanodisk array, (c) top view scheme of the hexagonal lattice, with the dashed rectangle showing one unit cell of the hexagonal lattice, as modeled in the computation.
• Figure 2: (a)-(d) Quasi-3D structure and its breakdown into components, as modelled in FDTD simulations (e)-(h) Transmittivity and reflectivity of the corresponding systems
• Figure 3: (a)-(b) Vertical map of E field localization (c)-(d) Horizontal map of E field localization, in the wavelength of resonance. The left column corresponds to the dielectric PhC at $\lambda_{resonance}\sim850 nm$ and The right column corresponds to the Quasi-3D structure at $\lambda_{resonance}\sim790 nm$.
• Figure 4: (a) Schematic representation of the fabrication process. (b) Real image of the sample showing the periodically patterned and the unpatterned part (c) Scanning electron microscope (SEM) image of the sample.
• Figure 5: (a) Schematics of the experimental set-up used to measure reflected third harmonic signals generated by the gold grating as a function of angle of incidence, polarization, and incident wavelength. (b) Schematic representation of to E field localization and THG at normal incidence (c)setup modification to detect the THG at normal or near normal incidence.