Strong chiral dichroism and enantiopurification in above-threshold ionization with locally chiral light

Abstract

We derive here a highly selective photoelectron-based chirality-sensing technique that utilizes “locally chiral” laser pulses. We show that this approach results in strong chiral discrimination, where the standard forwards/backwards asymmetry of photoelectron circular dichroism (PECD) is lifted. The resulting dichroism is larger and more robust than conventional PECD (especially in the high-energy part of the spectrum), is found in all hemispheres, and is not symmetric or antisymmetric with respect to any symmetry operator. Remarkably, chiral dichroism of up to 10% survives in the angularly integrated above-threshold ionization (ATI) spectra, and chiral dichroism of up to 5% survives in the total ionization rates. We demonstrate these results through ab initio calculations in the chiral molecules bromochlorofluoromethane, limonene, fenchone, and camphor. We also explore the parameter space of the locally chiral field and show that the observed dichroism is strongly correlated to the degree of chirality of the light, validating it as a measure for chiral-interaction strengths. Our results pave the way for highly selective probing of ultrafast chirality in ATI and motivate the use of locally chiral light for enhancing ultrafast spectroscopies. Most importantly, the technique can be implemented to achieve all-optical enantiopurification of chiral samples.

Umberto De Giovannini

Associate Professor

My research interests include ab-initio light matter interactions and numerical methods.