Chiral sensing with achiral anisotropic metasurfaces

We present a theoretical analysis for chiral sensing using achiral anisotropic metasurfaces. We derive analytically, and verify numerically, simple formulas that provide insight into the sensing mechanism and explain how anisotropic metasurfaces offer additional degrees of freedom with respect to their isotropic counterparts. We demonstrate how to deconvolve the unknown chirality from the background dispersion of the metasurface, and we propose practical measurement schemes for its unambiguous determination. Last, we discuss the key functionalities and benefits of anisotropic metasurfaces, and we provide the design principles towards broadband operation-from near-infrared to near-ultraviolet frequencies-opening the way for highly sensitive nanoscale chiroptical spectroscopy. Our numerical examples are focused on ametasurface design that we recently proposed, which belongs to the wider class of achiral anisotropic metasurfaces.