  Metasurfaces represent a powerful paradigm of optical engineering that
enables one to control the flow of light across material interfaces. We report
on a discovery that metallic metasurfaces of a certain type respond differently
to spatially coherent and incoherent light, enabling robust speckle-free
discrimination between different degrees of coherence. The effect has no direct
analogue in conventional optics and may find applications in compact
metadevices enhancing imaging, vision, detection, communication and metrology.
