# Nonlinear light conversion and infrared photodetection with laser-printed plasmonic metasurfaces supporting bound states in the continuum

## TL;DR

Researchers developed a laser-printed gold metasurface that supports special light interactions, enabling efficient infrared detection and nonlinear light conversion.

## Contribution

A scalable laser-printing method was used to fabricate plasmonic metasurfaces supporting symmetry-protected quasi-bound states in the continuum (qBIC) for nonlinear and photodetection applications.

## Key findings

- Laser-printed metasurfaces achieved a Q-factor up to 20 with symmetry-protected plasmonic quasi-bound states in the continuum.
- Third harmonic generation was enhanced by ≈105 compared to smooth gold films under critical coupling conditions.
- A qBIC-empowered field-effect transistor with HgTe quantum dots showed high detectivity and fast response in the infrared range.

## Abstract

Plasmonic metasurfaces supporting high-quality (Q) resonances offer unprecedented ways for controlling light-matter interaction at the nanoscale, yet scalable fabrication of such sophisticated nanostructures still relies on expensive and multi-step fabrication routes, hindering their practical application. Here, we produced plasmonic metasurfaces composed of the regular arrangement of hollow protruding nanobumps via direct femtosecond laser patterning of thin gold films. By using comprehensive optical modeling, infrared spectroscopy and angle-resolved third harmonic generation experiments, we justified that such laser-printed nanostructures support symmetry-protected plasmonic quasi-bound states in the continuum (qBIC) with a measured Q-factor up to 20. Moreover, under critical coupling conditions that match the radiative and nonradiative losses of the high-Q mode, the metasurfaces demonstrate the third harmonic generation enhanced by a factor of ≈105 as compared to the smooth Au film benchmark, proving structure efficiency for nonlinear conversion. Finally, by taking advantage of the simplicity and straightforward character of the laser printing process, we realized a field-effect transistor device with HgTe quantum dots as an active medium and qBIC-supporting plasmonic metasurface imprinted over drain and source electrodes. The resulting metasurface-empowered device operates at 200 K and 5 V bias voltage and demonstrates superior specific detectivity around 8.7 × 1011 at the plasmonic-qBIC spectral region and fast response time, holding promise for the realization of advanced shortwave infrared photodetectors.

Laser-printed gold metasurface supporting symmetry-protected plasmonic quasi-bound states in the continuum (qBIC) was fabricated, comprehensively characterized and applied to demonstrate the first qBIC-empowered field-effect transistor device with HgTe quantum dot active medium.