Interferometric control of the nonlinear optical emission at the nanoscale

The optical resonances of nanostructures have shown great potential to enhance and control nonlinear optical processes, which are intrinsically weak in ultrathin volumes. There is presently a strong drive towards reconfiguring the resonant response, enabling versatile or broadband functionalities. Among several proposed physical mechanisms (mechanical, thermal,…) all-optical approaches stand out for their fast switching and contactless operation. Pump–probe experiments have demonstrated various forms of intensity-based tuning, exploiting a transient alteration of the material properties. Phase, conversely, has received little attention as a potential control tool. We recently developed a two-pump scheme mixing a pulse at ω with its frequency-doubled replica. The resulting sum-frequency (ω+2ω) and third-harmonic emissions (ω+ω+ω) are coherent and degenerate at 3ω. Because of their opposite parity, their interference is enabled by a symmetry breaking—through directional filtering or by the nanostructure geometry. We reported recently (ArXiv:2307.01794) a 90% intensity modulation and directional routing by an AlGaAs metasurface controlled via the relative phase between the two pumps.