Enhanced chiral sensing using achiral metasurfaces with gain

The inherent weak nature of chiroptical signals provided by typical polarimetric measurements of natural optically active media has led to the development of different techniques to achieve enhanced chiral sensing. Intuitively, the introduction of gain could provide the desired enhancement; however, this requires gain media that can couple directly to the chiral medium. Here, it is shown that nanophotonic systems that generate collinear electric and magnetic dipole moments can mediate the coupling between the gain and chiral medium, leading to signals stronger than those achieved by the chiral medium alone or when combined with the same nanophotonic system without gain. Depending on how strongly gain couples with the nanophotonic system, both background amplification and loss compensation are possible. In this context, it also is shown that the enhancement occurs within the regime of loss compensation, because background amplification may also result in amplified transmitted fields, but does not guarantee the enhancement of chiroptical signals. (C) 2021 Optical Society of America