Molecular alignment induced by the near-infrared few-cycle laser pulse through nonresonant process

Molecular alignment and orientation are two special rotation states of gaseous molecules. Nowdays, molecular alignment and orientation has been a hot topic of atoms, molecules and optical physics since they not only can reveal the deep quantum mechanisms of the molecules in the external field but also pave a way for the quantum information science, intense field physics. Here, we investigate the molecular alignment of gaseous carbon monoxide (CO) induced by the near-infrared few-cycle laser pulses through nonresonant process by numerical methods. The Hamiltonian of the molecules in the ultrashort laser pulses is obtained based on the rigid rotor approximation theory, then the time-dependent Schrodinger equation of the system is solved by split-step Fourier transform. It is found that the momentum of the molecules increases rapidly in a very short time, and then keeps stably for a long time; the alignment degree of molecules is an oscillation signal in the time domain even the laser pulses have propagated away. The alignment degree is transformed into the frequency domain to explore the deep mechanisms. The relationship between the laser wavelength and the alignment degree is also discussed based on the simulation results. This work might help to understand the interactions between the gaseous diatomic molecules and few-cycle laser pulse.