Spin‐Controlled Nonlinear Harmonic Generations from Plasmonic Metasurfaces Coupled to Intersubband Transitions

Abstract Metasurfaces that generate nonlinear optical responses provide new degrees of freedom for applications such as nonlinear holography, wave mixing, and new frequencies generation. To extend the utility of flat nonlinear optics, metasurfaces providing both giant nonlinear response for efficient frequency mixing in subwavelength films and a single‐beam output with a local wavefront control need to be developed. Metasurfaces with giant nonlinear response have recently been realized using the concept of intersubband polaritons. Separately, nonlinear metasurfaces providing a single‐beam nonlinear output with a local wavefront control have been studied. However, a metasurface platform that possesses both of these properties has yet to be demonstrated. Herein, the first such platform is presented and its operation for three‐ and four‐wave mixing processes is demonstrated. This approach is based on using Pancharatnam–Berry phase control of local nonlinear response and on employing meta‐atoms with specific symmetries to enable generation of only a single nonlinear beam. Experimentally, 400 nm‐thick metasurfaces with a wavefront‐controlled single‐beam output are demonstrated for second‐ and third‐harmonic generation at pump wavelength of approximately 10 µm. Power conversion efficiencies of 7.6 × 10⁻⁴% and 3.6 × 10⁻⁴% are obtained for the two nonlinear processes, respectively, at peak pumping intensity of only 80 kW cm⁻².