Difference-Frequency Generation in Polaritonic Intersubband Nonlinear Metasurfaces

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 = 5.4 mu m photons are downconverted to lambda = 12.9 mu m 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.