Increasing ion yield circular dichroism in femtosecond photoionisation using optimal control theory

TL;DR

This paper demonstrates that optimal control theory can significantly enhance circular dichroism signals in femtosecond photoionization of chiral molecules, revealing new ways to amplify chiral signatures using shaped laser pulses.

Contribution

The study introduces a model incorporating multipole moments and shows how shaped laser pulses can increase CD signals by a factor of 3.5, advancing chiroptical measurement techniques.

Findings

CD signal increased by a factor of 3.5 with shaped pulses

Anisotropy parameter g increased from 0.06 to 1

Optimal control enhances chiral signal detection

Abstract

We investigate how optimal control theory can be used to improve Circular Dichroism (CD) signals for A--band of fenchone measured via the photoionization yield upon further excitation. These transitions are electric dipole forbidden to first order, which translates into low population transfer to the excited state (~8%) but also allows for a clearer interplay between electric and magnetic transition dipole moments, which are of the same order of magnitude. Using a model including the electronic ground and excited A state as well as all permanent and transition multipole moments up to the electric quadrupole, we find that the absolute CD signal of randomly oriented molecules can be increased by a factor 3.5 when using shaped laser pulses, with the anisotropy parameter g increasing from 0.06 to 1. Our insights provide additional evidence on how optimal control can assist in amplifying chiral signatures via interactions of permanent and transition multipole moments.