Chiral topological light for detecting robust enantio-sensitive observables

Topological response of matter to electromagnetic fields is the property in demand in materials design and metrology due to its robustness against the noise or decoherence, stimulating recent advances in ultrafast photonics. Similar topological robustness is desirable in enantio-sensitive detection but is currently missing. We introduce the concept of a chiral topological light - a hybrid between the vortex beam and synthetic chiral light, which interacts with chiral molecules extremely efficiently due to the electric dipole nature of this interaction. An integer topological charge is encoded in the azymuthal evolution of light's handedness. The topological protection arises due to mapping of topological charge into the intensity of the far-field profile of non-linear optical response, where enantio-sensitivity arises as its spatial rotation. The intensity maxima are robust against noise and enable detection of percent level enantiomeric excesses in mixtures as we demonstrate numerically for randomly oriented fenchone molecules. Next we show that using the topological charge as a parameter one can reconstruct the chiral and achiral components of non-linear response. Our work opens a way to the new extremely efficient and robust chiroptical spectroscopies with attosecond time resolution.