Ahiboz, D.; Manley, P.; Becker, C.: Adjustable large-area dielectric metasurfaces for near-normal oblique incident excitation. OSA Continuum 3 (2020), p. 971-981

We present large-area (25 cm2) dielectric metasurfaces based on silicon photonic crystal slabs. Adjustment of the slab thickness allows to systematically shift the metasurface resonances over several hundreds of nanometers. We compute the three-dimensional field energy density near the surface and determine optimum slab thicknesses for selected near-infrared excitation wavelengths applied in biophotonics. Our simulations reveal up to 17-fold enhanced near-field energy densities at normal incidence, but over 500-fold enhancement at 4° incident excitation. We explain this behaviour via the coupling of external radiation with symmetryprotected bound states in the continuum. These results enable metasurface-enhanced spectroscopy on large areas and underline the benefit of slight oblique incidence excitation conditions.