Enhanced chiroptical responses through coherent perfect absorption in a parity-time symmetric system

Coherent amplification of chiroptical activity from a molecularly-thin optically-active substance has been a long-standing challenge due to the inherently weak nature of chiral responses. Here we report how a coherent perfect absorber (CPA) enabled by an achiral optical system obeying parity-time (PT) symmetry has an enhanced ability to effectively sense molecular chirality of monolayered substances. We demonstrate that such a CPA-based PT-symmetric system enables us in complete darkness to probe a subtle signal change induced by the introduction of a small disturbance, such as adsorbed chiral monolayer, to the unperturbed PT-symmetric system, and allows for absolute measurement and quantitative detection of the magnitude and sign of both real and imaginary parts of the chirality parameter in a background-free environment. Moreover, the CPA-based PT-symmetric system also exhibits three orders of magnitude enhancement in chiroptical responses of molecules, which is consistent with analytical calculations of differential absorption. Optical sensors traditionally struggle to detect inherently weak chiral signals from molecules. Here, coherent perfect absorption in a parity-time symmetric platform is predicted to increase chiral sensitivity by three orders of magnitude.

Automated summary

By utilizing an achiral optical system obeying parity-time symmetry, coherent perfect absorption is predicted to significantly enhance the detection of molecular chirality, increasing the sensitivity to weak chiral signals by three orders of magnitude and allowing for accurate measurement of chiroptical parameters.