Determination of enantiomeric excess with chirality-dependent ac Stark effects in cyclic three-level models

Determination of enantiomeric excess is important and remains challenging. We propose theoretically a spectroscopic method for this issue based on the chirality-dependent ac Stark effects in cyclic three-level models under the three-photon resonance condition. The enantiomeric excess of the chiral mixture is determined by comparing the amplitudes of the two ac Stark peaks chosen in the Fourier transform spectrum of the induced polarizations, which are (approximately) proportional to the number of molecules of the two enantiomers, respectively. In contrast to current spectroscopic methods based on the interference between the electric and (usually weak) magnetic dipole transition moments and/or with the need for enantiopure samples, our method involves only electric dipole transitions and does not require the enantiopure samples. Therefore, it will give strong chiral signals and can be applied to the determination of enantiomeric excess for chiral molecules whose enantiopure samples are still challenging to achieve.