Investigation on gaseous molecular alignment echoes induced by the intense phase-tunable terahertz pulses

Intense broadband terahertz (THz) pulse has been used to align/orient gaseous molecules. Here the molecular alignment of gaseous carbon monoxide induced by the intense phase-tunable single-cycle THz pulse is studied based on the rigid rotor approximation theory and numerical methods. It is found that the alignment degree has an echo signal in the frequency domain depending on the intensity of THz pulse, which is mainly induced by the momentum transition of the molecules excited by the THz field. The alignment is also a period function of the phase of the THz pulses. Thus, the alignment degree is controlled by the changing of the phase of THz pulses. Our work offers a theoretical reference to control the molecule alignment by the intense THz pulses and might help to reveal the quantum rotational states of gaseous molecules.