Angular shift of Autler–Townes doublet from multi-photon ionization of molecules by circularly polarized laser pulses

Abstract

Abstract We theoretically study the Autler–Townes (AT) splitting of a molecule in a circularly polarized laser pulse by solving the time-dependent Schrödinger equation. We find that the AT doublet in the photoelectron momentum distribution reveals different angular shifts with respect to the molecular axis direction. Using an improved strong-field approximation method, we reproduce the difference of the angular shifts for the AT doublet, which originates from the interference of the electron wave packets released from the ground and excited states of the molecule. By tracing the time evolution of the electron density distribution along the molecular axis, we find that electron delocalization on the two nuclei of the molecule plays a significant role in the formation of photoelectron angular distribution for the AT doublet, which corresponds to a phase jump of π for the phase difference between the ground and excited states.