Handedness-Selective Nonlinear Absorption of a Chiral Metasurface Empowered by an Intelligent Distribution Algorithm

Chiral metasurfaces, as planar or quasi-planar photonic nanostructures composed of artificial meta-atoms at the sub-wavelength scale, exhibit significant chiral optical responses in near-field and/or far-field regions. They find essential applications in linear regime including optical chiral sensing and chiral particle separation, as well as in nonlinear regime such as ultrafast chiral modulation. This work investigates handedness-dependent two-photon absorption effect of a chiral metasurface, which comprises periodic asymmetric split ring amorphous silicon (α-Si) nanostructure atop, an optically thin silica spacer layer, and a gold-film mirror at the bottom. The metasurface was inversely designed by using a distributed algorithm that combines distributed strategy, genetic algorithm, and finite difference time domain (FDTD) simulation method. Pronounced chiral selectivity in both linear (circular dichroism up to −0.56 at the wavelength of 1040 nm) and nonlinear (two-photon absorption, shortly TPA, with non-saturable absorption coefficient {{\beta }_0} of 4 orders of magnitude larger than bulk Si) regimes are experimentally achieved. The intelligent algorithm empowered nonlinear chiral metasurface may provide new perspectives towards nonlinear chiral sensing, imaging, and optical switching, controlled by handedness of the impinging light.