Nonlinear dielectric metasurfaces: Towards high efficiency and full spatial phase control

Metasurfaces are ideally suited for nonlinear optical processes due to their relaxation of the phase-matching condition. This opens the possibility to generate and alter the wavefront of nonlinear harmonic generation beams. However, the short propagation distance through the metasurface limits the conversion efficiency. Here, we discuss concepts of tailoring the spatial phase together with high efficiency of harmonic signals generated by silicon metasurfaces.