Chirality-assisted lateral momentum transfer for bidirectional enantioselective separation

• Main Authors: Shi, Yuzhi, Zhu, Tongtong, Zhang, Tianhang, Mazzulla, Alfredo, Tsai, Din Ping, Ding, Weiqiang, Liu, Ai Qun, Cipparrone, Gabriella, Sáenz, Juan José, Qiu, Cheng-Wei
• Other Authors: School of Electrical and Electronic Engineering
• Format: Article
• Language: English
• Published: 2021
• Subjects: Science::Physics; Applied Optics; Optical Manipulation and Tweezers
• Online Access: https://hdl.handle.net/10356/147276
• Institution: Nanyang Technological University

Lateral optical forces induced by linearly polarized laser beams have been predicted to deflect dipolar particles with opposite chiralities toward opposite transversal directions. These "chirality-dependent" forces can offer new possibilities for passive all-optical enantioselective sorting of chiral particles, which is essential to the nanoscience and drug industries. However, previous chiral sorting experiments focused on large particles with diameters in the geometrical-optics regime. Here, we demonstrate, for the first time, the robust sorting of Mie (size ~ wavelength) chiral particles with different handedness at an air-water interface using optical lateral forces induced by a single linearly polarized laser beam. The nontrivial physical interactions underlying these chirality-dependent forces distinctly differ from those predicted for dipolar or geometrical-optics particles. The lateral forces emerge from a complex interplay between the light polarization, lateral momentum enhancement, and out-of-plane light refraction at the particle-water interface. The sign of the lateral force could be reversed by changing the particle size, incident angle, and polarization of the obliquely incident light.