Enantioselective transport of chiral spheres using focused femtosecond laser pulses.

Optical tweezers are commonly used for manipulating chiral particles by tailoring the properties of the electromagnetic field or of the particles themselves. Non-linearity provides additional degree of freedom to control the manipulation by changing the trapping conditions. In this work, we leverage the nonlinear optical properties of a medium by illuminating it with a circularly polarized laser pulse, enabling single particle enantioselection for the chiral spheres immersed in it. By adjusting the power of the laser pulses, we demonstrate stable trapping of chiral spheres with one handedness near the focal region, while spheres with the opposite handedness are repelled. This enables the chiral resolution of racemic mixtures. Additionally, we perturbed the stable equilibrium position of the trap by driving the sample stage, leading to the emergence of a new stable equilibrium position achieved under the action of the Stokes force. Here we show that the chirality of each individually trapped particle can also be characterized by the rotation of the equilibrium position. Since the power of the laser pulses can be experimentally controlled, this scheme is practical to perform enantioselection, chiral characterization, and chiral resolution of a single chiral sphere with arbitrarily small chirality parameters.