Third‐Harmonic Generation from Plasmonic Metasurfaces Coupled to Intersubband Transitions

Abstract Nonlinear responses in metasurfaces have shown great promise for various applications, such as nonlinear holography, spectroscopy, and novel nonlinear light sources. Metasurfaces that produce nonlinear responses have the advantage of greatly relaxed phase‐matching conditions, which can simplify nonlinear optical systems. However, the practical use of nonlinear metasurfaces with an accessible optical pump source requires giant nonlinear responses. A multi‐quantum‐well‐loaded nonlinear metasurface designed for third‐harmonic generation at λ ≈ 8.9 µm with a record‐high third‐order nonlinear optical response is presented for condensed matter systems in the infrared spectral range of up to 4.4 × 10⁻¹⁴ m² V⁻². About 1.8 × 10⁻³% third‐harmonic generation power conversion efficiency is experimentally achieved in 400 nm thick metasurfaces with a pump intensity of only 210 kW cm⁻². The multi‐quantum‐well structure can be used to produce second‐harmonic generation when combined with properly designed nanoresonators to allow multiple and simultaneous harmonic generations on the same chip.