4000-enhancement of difference frequency generation in a mode-matching metamaterial

In the wake of the control of light at the sub-wavelength scale by nanoresonators, metasurfaces allowing strong field exaltations are an attractive platform to enhance nonlinear processes. Recently, high efficiency second harmonic and difference frequency generations were demonstrated in metasurfaces that generate a nonlinear polarization normal to the surface. Here, we introduce a mode matched resonator that is able to produce this particular nonlinear polarization in a layer of gallium arsenide associated with a gold metasurface. The nonlinear conversion mechanism is described as a two-step process in which efficiency is shown to yield a good colocalization and a strong enhancement of the pump fields, as well as a high extraction efficiency of the generated field. This mode-matched metasurface is able to reach a difference frequency generation (DFG) efficiency of 10⁻²W/W². This opens a new paradigm where alternative nonlinear materials could be reintroduced in metasurfaces and yields even higher efficiency than high effective χ⁽2⁾ structures.