Amplified linear and nonlinear chiral sensing assisted by anapole modes in hybrid metasurfaces

The interaction between chiral molecules and circularly polarized light is largely influenced by the local optical chirality density. This interaction prompts a substantial demand of the design of nanophotonic platforms capable of enhancing such effects across large and accessible volumes. Such a magnification requires nanostructures to provide high electric and magnetic field enhancements while keeping the phase relation of circular light. Dielectric nanostructures, particularly those able to support resonances, are uniquely suited for this task due to their capacity for high electric and magnetic field enhancements. On the other hand, efficient third harmonic generation calls for strong electric field resonances within dielectric materials, a feature often boosted by incorporating plasmonic materials into hybrid systems. In this numerical study, we propose a coupled silicon disk-gold ring system that can exploit the anapole-induced field confinement to provide a broadband magnified circular dichroism under realistic conditions, reaching values up to a 5-fold enhancement. We also demonstrate that this structure can be employed as an efficient third harmonic generator which, when integrated with chiral media, enables a 10-fold enhancement in circular dichroism. Furthermore, we numerically show that pulsed illumination at intensities up to 10 GW/cm2 does not induce temperature increments that could potentially damage the samples. These findings suggest that this system can be a promising and versatile approach towards ultrasensitive background-free chiral sensing.