Long-lived field-free molecular orientation driven by modulated few-cycle terahertz pulses

The influence of molecular alignment and orientation in the ground state and excited state on the resonance-enhanced multi-photon ionization dynamics

We explore the influence of molecular alignment and orientation in the ground and excited states on the ionization probability, photoelectron angular distribution (PAD), energy-resolved photoelectron energy spectrum (PES) and two-dimensional momentum spectrum in the resonance-enhanced multiphoton ionization (REMPI) process. The calculated results for the LiH molecule show that molecular pre-alignment and -orientation have different effects on molecular photoionization. The ionization probability and energy-resolved photoelectron spectrum are associated with molecular pre-alignment. The angular distribution of photoelectrons and angular distribution of the momentum spectra are closely dependent on molecular pre-orientation. The ionization probability is also related to the center time and overlap area of the pump and probe pulses.

The photoionization dynamics based on molecular pre-orientation

We study theoretically the photoionization dynamics of pre-oriented NaK molecule. Firstly, a THz laser pulse is utilized to orient the ground state molecule. And then the pump and probe laser pulses are used to excite and ionize the molecule, respectively. We study the influence of molecular orientation duration and degree on the ionization probability, angle-resolved photoelectron spectrum and photoelectron angular distribution (PAD). It is shown that we could obtain more stable ionization signal and PAD when the molecules are ionized in molecular orientation duration. We could increase the ionization probability and obtain more concentrated ionization signal and photoelectron distribution by increasing the orientation degree in the ground state. Moreover, we discuss the splitting pattern in the angle-resolved photoelectron spectrum.