Difference‐Frequency Generation in Polaritonic Intersubband Nonlinear Metasurfaces

Abstract A nonlinear intersubband polaritonic metasurface designed for difference‐frequency generation that provides a practical level of nonlinear response under continuous wave illumination is reported. An effective nonlinear susceptibility of up to 340 nm V⁻¹ is measured experimentally. Approximately 0.3% of λ = 5.4 µm photons are downconverted to λ = 12.9 µm photons at the focal spot in the experiment. This work indicates that the ultrathin metasurface devices may provide a versatile nonlinear element for frequency down‐ and upconversion in a relatively broad spectral range and without phase‐matching constrains of traditional bulk nonlinear crystals.