Perfect All-Angular Nonlocal Metasurfaces via the Generalized Huygens' Condition

We highlight the importance of the recently derived generalized Huygens' condition in realizing physically-meaningful nonlocal metasurfaces (MSs) with optimal performance across the entire (visible) spatial spectrum. The pivotal role of the corresponding (normal-susceptbility-enabled) grazing angle Huygens' condition is demonstrated by the synthesis of a symmetric omnidirectionally reflectionless MS for radome applications and an asymmetric spatial differentiator for analog computing, verified via full-wave solvers. For the symmetric case, direct closed-form translation of the required surface susceptibility tensor into an impedance sheet cascade is formulated, facilitating experimental validation. These results pave the path towards a systematic framework for devising versatile, realistic and efficient, nonlocal MSs.