Continuous wave second harmonic generation enabled by quasi-bound-states in the continuum on gallium phosphide metasurfaces

TL;DR

This paper demonstrates continuous wave second harmonic generation in gallium phosphide metasurfaces using bound states in the continuum, achieving higher efficiencies at lower pump intensities than previous dielectric metasurfaces.

Contribution

It introduces a novel approach combining gallium phosphide with bound states in the continuum to enable efficient CW SHG with lower pump intensities.

Findings

Achieved ~5e-5% W$^{-1}$ efficiency at 1200 nm with 1 kW/cm$^2$ CW pump.

Measured external efficiency up to 0.1% W$^{-1}$ with pulsed pump at 10 MW/cm$^2$.

Demonstrated higher efficiency at lower pump intensities compared to prior dielectric metasurfaces.

Abstract

Resonant metasurfaces are an attractive platform for enhancing the non-linear optical processes, such as second harmonic generation (SHG), since they can generate very large local electromagnetic fields while relaxing the phase-matching requirements. Here, we take this platform a step closer to the practical applications by demonstrating visible range, continuous wave (CW) SHG. We do so by combining the attractive material properties of gallium phosphide with engineered, high quality-factor photonic modes enabled by bound states in the continuum. For the optimum case, we obtain efficiencies around 5e-5 % W$^{-1}$ when the system is pumped at 1200 nm wavelength with CW intensities of 1 kW/cm$^2$. Moreover, we measure external efficiencies as high as 0.1 % W$^{-1}$ with pump intensities of only 10 MW/cm$^2$ for pulsed irradiation. This efficiency is higher than the values previously reported for dielectric metasurfaces, but achieved here with pump intensities that are two orders of magnitude lower.