Highly selective chiral discrimination in high harmonic generation by dynamical symmetry breaking spectroscopy

TL;DR

This paper introduces a robust, highly selective femtosecond chiral spectroscopy method using high harmonic generation that relies on dynamical symmetry breaking, enabling direct correlation between forbidden harmonic intensity and enantiomeric excess.

Contribution

The authors propose a novel chiral spectroscopy technique based on symmetry breaking in HHG, which does not require electric-magnetic dipole interplay and provides high selectivity with a single measurement.

Findings

Achieved 96% discrimination in gas-phase chiral media.

Demonstrated robustness and high selectivity of the method.

Outperforms previous time-resolved chiral spectroscopy techniques.

Abstract

We propose and numerically demonstrate a new very robust and highly selective method for femtosecond time-resolved chiral spectroscopy using high harmonic generation (HHG). The method is based on dynamical symmetry breaking from chiral media, and relies only on intense electric-dipole transitions, and not on the interplay of electric and magnetic dipoles. The symmetry breaking results in the emission of a strong chiral signal in the form of otherwise 'forbidden' harmonics (i.e., that are not emitted from achiral media). The intensity of these symmetry-forbidden harmonics is directly correlated to the media's enantiomeric excess, yielding chiral selectivity. On the contrary, the strength of the 'allowed' harmonics is chiral-independent, hence they can be used as a reference to provide chiral selectivity from a single measurement, unlike previous time-resolved schemes that require multiple measurements. We demonstrate numerically 96% discrimination level from microscopic gas phase emission, outperforming by far previous time-resolved methods (the selectivity should be further enhanced when the HHG process is phase matched). We expect the new method to give rise to precise table-top characterization of chiral media in the gas-phase, and for highly sensitive time-resolved ultrafast probing of dynamical chiral processes.