Intrinsic chiral discrimination via terahertz absorption circular dichroism

Abstract

Identifying chiral molecules and accurately resolving their enantiomeric characteristics in the terahertz (THz) regime remains challenging due to intrinsically weak circular dichroism (CD) signals. Most existing THz-CD studies have relied on transmission amplitude differences, which are susceptible to severe signal attenuation and spectral distortion in lossy or strongly absorbing media. In this work, we present an alternative approach that retrieves helicity-dependent absorption coefficients from the complex transmission function, obtained through polarization-resolved THz time-domain spectroscopy. By analyzing the difference between the extracted absorption spectra for right and left circularly polarized THz waves, we obtain an absorption-resolved CD signal that reflects the intrinsic chiroptical asymmetry of the sample. We validate this method using two representative chiral molecules, glucose and tartaric acid, whose enantiomers exhibit bisignate CD spectral features centered at 1.45 and 1.1 THz, respectively, corresponding to their molecular resonances. These spectral signatures, which are obscured in transmission-based CD measurements, become distinctly observable through our absorption-based analysis. This label-free and quantitative approach provides a robust platform for chiral sensing and is applicable to pharmaceutical analysis, biochemical diagnostics, and molecular spectroscopy.