Chiral sensing with achiral anisotropic metasurfaces

Recently, we proposed a metasurface design for chiral sensing that (i) results in enhanced chiroptical signals by more than two orders of magnitude ultrathin, subwavelength, samples over uniform and accessible area, (ii) allows complete measurements the total chirality (magnitude sign both its real imaginary part), (iii) offers possibility crucial signal reversal (excitation with reversed polarization) enables an absolute manner, i.e., without need sample removal. Our is based on anisotropic response metasurface, rather superchirality generated near-fields, as most contemporary nanophotonic-based approaches. Here, derive analytically, verify numerically, simple formulas provide insight to mechanism explain how metasurfaces, general, offer additional degrees freedom respect their isotropic counterparts. We detailed discussion key functionalities benefits our demonstrate practical measurement schemes unambiguous determination unknown chirality. Last, principles towards broadband operation - from near-infrared near-ultraviolet frequencies opening way highly sensitive nanoscale spectroscopy.