Enantiospecific two-photon electric-dipole selection rule of chiral molecules

Distinguishing between enantiomers is crucial in chemistry and pharmacology. Existing optical methods rely on enantiospecific three-photon electric-dipole transitions, requiring phase locking, three-photon resonance, and precise beam control, limiting their practicality. Here, we propose an optical method that eliminates these constraints by applying a static electric field, which breaks a symmetry combining rotation and time reversal, leading to distinct two-photon selection rules for enantiomers. This enables selective excitation of a target enantiomer using two beams without phase locking or intensity control, greatly improving the feasibility of optical enantiomer differentiation.