Optical metasurfaces, i.e. two-dimensional arrangements of closely packed resonant nanostructures, have been recently proposed for the manipulation and steering of light. In particular, metasurfaces have the prospect of enhancing the optical nonlinearities at the nanoscale, thus opening new opportunities for Nonlinear Photonics. However, the research in the field has mostly concerned isotropic configurations of the metaatoms, whereas nonlinear anisotropic metasurfaces have been so far overlooked.
Here we report on the experimental and theoretical study of all-dielectric (semiconductor based) anisotropic metasurfaces interacting with intense fs-laser pulses. Broad-band pump-probe spectroscopy and semiclassical modeling of the photoinduced carriers enabled us to identify and disentangle the physical processes that govern the transient optical response of this kind of nanomaterials. Most interestingly, the observed ultrafast switching of the optical response can be independently engineered for orthogonal polarizations using the large shape-induced anisotropy, thus allowing ultrafast control of the giant optical dichroism of the metasurface.
Our results categorically ascertain the potential of shape induced optical anisotropy in nonlinear all-dielectric metasurfaces for the ultrafast control of optical dichroism and light polarization.