  Plasmonic metasurfaces have spawned the field of flat optics using
nanostructured planar metallic or dielectric surfaces that can replace bulky
optical elements and enhance the capabilities of traditional far-field optics.
Furthermore, the potential of flat optics can go far beyond far-field
modulation, and can be exploited for functionality in the near-field itself.
Here, we design metasurfaces based on aperiodic arrays of plasmonic Au
nanostructures for tailoring the optical near-field in the visible and
near-infrared spectral range. The basic element of the arrays is a rhomboid
that is modulated in size, orientation and position to achieve the desired
functionality of the micron-size metasurface structure. Using
two-photon-photoluminescence as a tool to probethe near-field profiles in the
plane of the metasurfaces, we demonstrate the molding of light into different
near-field intensity patterns and active pattern control via the far-field
illumination. Finite element method simulations reveal that the near-field
modulation occurs via a combination of the plasmonic resonances of the
rhomboids and field enhancement in the nanoscale gaps in between the elements.
This approach enables optical elements that can switch the near-field
distribution across the metasurface via wavelength and polarization of the
incident far-field light, and provides pathways for light matter interaction in
integrated devices.
