Turning elliptically polarized light into a highly efficient chiro-optical tool

Distinguishing the two opposite versions of a chiral molecule (enantiomers) is important in organic chemistry, materials science or biomedicine. However, chiral discrimination is challenging and requires an interaction with another chiral object. Chiral light, such as circularly or elliptically polarized light, has long served as a convenient tool for detecting the chirality of matter, but the chiro-optical signal is extremely weak because it relies on the interplay with the magnetic-field component of the wave. 

Here we show that tight focusing can turn elliptically polarized light into an efficient chiro-optical tool. When an elliptically polarized wave is tightly focused, its polarization plane is rotated towards the propagation direction. Interestingly, this polarization tilt is opposite at opposite sides of the beam axis. Using short laser pulses, this chiral structure allows us to distinguish between enantiomers via purely electric-dipole interactions. Our numerical modelling shows that the interaction of chiral molecules with such light leads to an enantio-sensitive bending of the nonlinear optical response: opposite enantiomers emit high-harmonics in opposite directions, creating new opportunities for imaging molecular chirality efficiently and on ultrafast time scales.