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

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.